METANANO 2021 Conference Program

Excitons are bound pairs of excited electrons and holes and play a crucial role in many photophysics processes occurring in Nature, such as photosynthesis and light absorption in organic and inorganic semiconductor materials. On the other hand, one of the most important phenomena in Quantum Electro-Dynamics (QED) is the so-called ``Strong Coupling’’ regime, which appears when the interaction between light and excitons in matter is so strong that the photon and matter components mix to create hybrid light/matter states, called polaritons. Traditionally, this hybrid character has been used to achieve new functionalities in which polaritons are thought of as dressed photons, e.g. by exploiting exciton-exciton coupling to construct interacting photons. However, over the last years, it has become clear that the strong coupling regime can be used with an alternative purpose: to significantly modify internal material properties and dynamics by dressing the excitons. In this keynote talk I plan to illustrate how the merging of these two fields of research (Excitons and QED) allows managing excitons to enhance energy transport in organic materials by taking advantage of the delocalized character of the polaritons and to alter the energy landscape of the organic molecules in such a way that photochemical reactions and even ground-state chemical reactions can be altered.

Microcavities are structures composed of two mirrors that are placed either side of a semiconductor thin film. Within the strong-coupling regime, a hybridization occurs between confined photon modes and the semiconductor excitons, creating new types of quasi-particles called cavity polaritons. As cavity polaritons are bosons, they can undergo a condensation process at high occupation density, creating a non-equilibrium polariton condensate that is trapped at the bottom of the polariton dispersion curve. The emission of light from such condensates carries the same high degree of spatial and temporal coherence as the condensate itself, and represents a class of light-source called a polariton laser. Firstly, I present recent work on the fabrication of strongly-coupled microcavities based on the organic dye BODIPY. I present evidence for polariton condensation in BODIPY-based microcavities, and demonstrate that condensates have a high degree of spatial coherence (up to 30 m), temporal coherence (up to 1.2 ns), with their emission energy being tunable through 125 meV by controlling cavity length. I then show that polariton condensation and lasing can be observed in cavities based on relatively simple cavity mirrors. I then present microcavities in which a periodic lattice of defects has been written into the active cavity layer using a serial optical patterning technique. Using a combination of Fourier-space imaging together with optical tomography, we characterize the fluorescence emission from the cavity, and show that a full 2D band-structure of the optical lattice within the cavity can be clearly evidenced.

Recent experiments [1-8] have demonstrated strong light–matter coupling between electromagnetic nanoresonators and pristine sheets of two-dimensional semiconductors, and it has been speculated whether these systems can enter the quantum regime operating at the few-polariton level. To address this question, we present a first-principles microscopic quantum theory [9] for the interaction between excitons in an infinite sheet of two-dimensional material and a localised electromagnetic resonator. We find that the light-matter interaction breaks the symmetry of the otherwise translation-invariant system and thereby effectively generates a localised exciton mode, which is coupled to an environment of residual exciton modes. This dissipative coupling increases with tighter lateral confinement, and our analysis reveals this to be a potential challenge in realising nonlinear exciton-exciton interaction. Nonetheless, we predict that polariton blockade due to nonlinear exciton-exciton interactions is well within reach for nanoresonators coupled to transition-metal dichalcogenides, provided that the lateral resonator mode confinement can be sufficiently small that the nonlinearity overcomes the polariton dephasing caused by phonon interactions [10]. [1] J. Wen, et al., Nano Letters 17, 4689 (2017). [2] D. Zheng et al., Nano Letters 17, 3809 (2017). [3] M.-E. Kleemann et al., Nature Communications 8, 1 (2017). [4] J. Cuadra et al., Nano Letters 18, 1777 (2018). [5] M. Stührenberg et al., Nano Letters 18, 5938 (2018). [6] X. Han et al., ACS Photonics 5, 3970 (2018). [7] M. Geisler et al., ACS Photonics 6, 994 (2019). [8] J. Qin, et al., Physical Review Letters 124, 063902 (2020). [9] E. V. Denning et al., arXiv:2103.14488 (2021). [10] E. V. Denning et al., arXiv:2103.14484 (2021).

Polydopamine (PDA) is one of the promising materials of modern nanotechnology, possessing record high adhesion, chemical stability, high oxidative capacity, and biocompatibility. However, PDA was found to be a fluorescence quencher by Foerster resonance energy transfer and/or photoinduced electron transfer mechanisms, which may affect the fluorescence intensity of the attached dye molecules. In this work, we show that the quenching can be significantly suppressed due to the formation of a strong coupling of dye molecules in PDA shell grown around plasmonic nanoparticle. In this case, the energy exchange between the dye molecules and the plasmon nanoparticle takes place at times much faster than the characteristic times of dye molecules quenching inside the of PDA material alone (without plasmonic nanoparticle). This makes it possible to weaken the quenching process of the dye molecules in the PDA shell by about 1000 times when the strong coupling limits are reached. Besides we show that the implementation of a strong optical coupling in such a system makes it possible to reach 30-fold reduction of dye molecules photodegradation process, which is a fundamental limitation of the use of dye molecules in nanophotonics and optical sensorics.

Nonlinear optical phenomena are central to a myriad of applications in light sources and microscopy. Nonlinear optical effects are fundamentally enhanced in materials with a high refractive index, following the so-called Miller’s rule, as well as by the presence of a resonant photonic environment. This has triggered a quest for nonlinearity enhancement in nanoscale resonators, where resonant dielectric metasurfaces play a key role. However, the applicability of high-index single-crystal metasurfaces for an enhanced nonlinear light generation has remained limited. This is hindered by difficulties in the fabrication of nanostructures from high-index crystalline materials on a transparent substrate, as well as by the strongly diffractive nature of the nonlinear harmonic generation, e.g. emission at multiple diffractive orders. In this talk, we present the use of different dielectric materials for nonlinear applications of metasurfaces, including III-V semiconductors, transition-metal-dichalcogenides and lithium niobate. We further demonstrate how the process of sum-frequency mixing of an infrared image with a homogeneous pump beam in GaAs resonant metasurfaces can result in coherent infrared to visible conversion of images for infrared imaging applications. Our results open new opportunities for the development of compact night-vision devices operating at room temperature and have multiple applications in defence and life sciences.

Recently it was shown that nonlinear metasurfaces can be used to generate broadband THz radiation. Here I will discuss different generation mechanisms, their selection rules, and show that complete spatiotemporal control over the polarization and phase of the THz waves is obtained, allowing a new class of functional and spin controlled THz emitters.

Optical angular momentum-based photonic technologies demonstrate the key role of the optical spin–orbit interaction that usually refers to linear optical processes in spatially engineered optical materials. Re-examining the basics of nonlinear optics of homogeneous crystals under circularly polarized light, we report experiments on the enrichment of the spin–orbit angular momentum spectrum of paraxial light. The demonstration is made within the framework of second-harmonic generation using a crystal with three-fold rotational symmetry. Four spin–orbit optical states for the second harmonic field are predicted from a single fundamental state owing to the interplay between linear spin–orbit coupling and nonlinear wave mixing; three of these states are experimentally verified. Besides representing a spin-controlled nonlinear route to orbital angular multiplexing, modal vortex light sources, high-dimensional parametric processes and multi-state optical magnetization, our findings suggest that the fundamentals of nonlinear optics are worth revisiting through the prism of the spin–orbit interaction of light.

We report on the development of a new approach for studying the internal structure of polymer integrated nanophotonics devices using phase-sensitive optical coherence microscopy. Visualization and flaw detection of devices and their internal structure was carried out using the example of coupling gratings and prisms for a miniature Otto configuration with a characteristic gap height of 50-300 nm.

Flat optical devices based on semiconductor nanostructures are considered a potentially powerful tool for processing optical information. However, these elements are mostly passive and cannot provide tunable operation. In this work, we develop and numerically investigate reconfigurable metasurfaces based on GaAs material, which can be switched between different amplitude-phase profiles under asymmetric optical pumping. We demonstrate the possibility to use them as a tunable Fourier filter for image processing tasks. Achieved results can open the way to create optical computing devices that are lightweight, compact, and remarkably fast compared to conventional analogues.

In this contribution, we present the analysis and numerical verification of the scattering phenomenon from a temporal interface in a parallel-plate waveguide realized by suddenly modifying the dimensions of the waveguide while the wave is propagating. As it is well known in guided wave theory, at the interface between two different waveguides there exists a change of the effective refractive index and wave impedance perceived by the propagating wave within the device, which inevitably scatters at the interface into a reflected and refracted wave. In analogous way, by suddenly changing the effective material properties within the whole waveguide, it is possible to realize the so-called temporal interface, as well. Here, we theoretically and numerically investigate on the scattering from a waveguide temporal interface induced by the abrupt change of the waveguide dimension, which in turn realize a change of the effective material properties perceived by the wave.

Many areas of major interest in Science and Engineering require one to solve infinite-dimensional optimization problems, also called functional optimization problems. In such a context, one has to minimize (or maximize) a functional with respect to admissible solutions belonging to infinite-dimensional spaces of functions, often dependent on a large number of variables. This is the case, for example, with analysis and design of large-scale networks, stochastic optimal control of nonlinear dynamic systems with a large number of state variables, optimal management of complex team organizations, freeway traffic congestion control, reconstruction of unknown environments, Web exploration, etc. Functional optimization problems can be solved analytically only if special assumptions are verified. When optimal solutions cannot be found analytically and/or numerical solutions are not easily implementable, classical approaches to find approximate solutions often incur the so-called “curse of dimensionality” (e.g., an extremely fast growth - with respect to the number d of variables of the admissible solutions - of the computational load required to obtain suboptimal solutions within a desired accuracy). The approximate method that we discuss is based on two steps. First, the decision functions are constrained to take on the structure of linear combinations of basis functions containing free parameters to be optimized. This approximation scheme, which is an extension to the Ritz method (for which fixed basis approximating functions) are used, is called “variable-basis approximation” and models a large variety of connectionistic models used in machine learning (e.g., neural networks, radial basis functions, etc.). Then, the functional optimization problem can be approximated by nonlinear programming problems. For certain classes of functional optimization problems, using variable.-basis connectionistic models may require a number of parameters increasing moderately with the number d of variables, whereas classical fixed-basis approximation may be ruled out by the curse of dimensionality.

During fabrication of photonic integrated circuits (ICs), the performance of each chip is being improved. The main method for this is the topology optimization (TO) of photonic devices. Previous studies have mainly relied on the TO application on a rectangular grid and did not take into account the limitations of a nanofab. Thus, structures could not be produced whose target optimization functions would not be subject to the stage of modifications (due to the adjustment of the device mask discretization to the nanofab constraints) following the TO. In addition, well-known software packages (such as Synopsys FullWave) require a lot of computing resources. We propose a new TO approach for passive components of photonic ICs (PICs) using machine learning and GFIEM (Green's Function Integral Equation Method), which uses GPGPU-accelerated implementation of GMRES (Generalized Minimal Residuals Method). The proposed software package showed this TO approach computation time is significantly less compared to Synopsys FullWave and takes into account the requirements of nanofab sampling. It can be applied in addition to existing programs as a utility. Analysis of world experience shows reducing the cost and increasing the competitiveness of devices and equipment are primarily associated with the transition from electronic ICs to PICs and with a TO usage of devices. The proposed TO approach promotes a faster transition to photonic PICs and enables to accelerate a PIC fabrication, reduce its size as well as the cost.

In this work, we corrected a parabolic X-Ray lens model, taking into account the voxel size. In the simplest case for constant laser power, the problem can be solved analytically. To prove the corrected model's efficiency, we compared the vertical sections of lenses printed with and without correction. To conclude, we have corrected the 3D model of the parabolic lens for direct laser writing (DLW). The research can be helpful for further advance of DLW-fabrication of X-Ray optical elements.

A promising technique for the spectral design of acoustic metamaterials is based on the formulation of suitable constrained nonlinear optimization problems. Unfortunately, the straightforward application of classical gradient-based iterative optimization algorithms to the numerical solution of such problems is typically highly demanding, due to the complexity of the underlying physical models. Nevertheless, supervised machine learning techniques can reduce such a computational effort, e.g., by replacing the original objective functions of such optimization problems with more-easily computable approximations. In this framework, the present article describes the application of a related unsupervised machine learning technique, namely, principal component analysis, to approximate the gradient of the objective function of a band gap optimization problem for an acoustic metamaterial, with the aim of making the successive application of a gradient-based iterative optimization algorithm faster. Numerical results show the effectiveness of the proposed method (joint work with Andrea Bacigalupo, Francesca Fantoni, Daniela Selvi).

Focus is on the design of an innovative class of tunable periodic metamaterials, conceived for the realization of high performance acoustic metafilters with settable real-time capabilities. In this framework the tunability is due to the presence of a piezoelectric phase shunted by a suitable electrical circuit with adjustable impedance/admittance. It follows that the acoustic properties of the metamaterial can be properly modified in an adaptive way, opening up new possibilities for the control of pass- and stop-bands.

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Fluorescence of the modified GFP chromophore diethyl-ABDI-BF2 dispersed in PMMA matrix is studied on top of glass, continuous and perforated optically thin silver films. In polymer, the fluorescence decay kinetics becomes non-exponential and can be described by the distribution of rate constants. The results demonstrate shortening of the excited state lifetime in the presence of silver and broadening of the lifetime distribution caused by the nanoholes.

An environment-friendly method of pulsed laser ablation in liquids is successfully employed for structural modification of silicon nanoparticles leading to considerable narrowing of their size distribution accompanied with reduction of the mean size. Contamination-free conditions of synthesis ensure the chemical purity of formed nanostructures that may reduce toxicity issues. Such a laser-induced modification leads to the appearance of plasmonic properties in semiconductor-based nanomaterials. Their spectral position can easily be varied in the whole visible range. Combined in one nanoparticle properties of semiconductors and noble metals can strongly promote applications of composite laser-synthesized nanoparticles for biosensing (using their plasmonic-based surface-enhanced ability) and bioimaging (using their both optical and magnetic abilities) purposes.

Using direct femtosecond laser patterning of metal-insulator-metal sandwich designed to support Fabry-Perot mode in the visible spectral range we demonstrate new practically relevant strategy for high-resolution color printing. Up-scalable ablation-free laser fabrication method paves the way towards various applications ranging from large-scale structural color printing at a lateral resolution of 25,000 dots per inch.

In spite of the presence of exact analytic and numerical solutions, the popularity of alternative intuitive description of light scattering, and other plasmonic properties, in more simple terms appears to be greater than ever before. Our works reports on new and important development of the so-called modified long wavelength approximation (MLWA), which has been known to very accurately approximate the T-matrix by a simple ratio $iR/(F+D-iR)$, where $F$ is a size-independent Fr\"ohlich term, $R$ is a radiative reaction term, and $D$ is a dynamic depolarization term. With $F$ and $R$ fixed, our main finding is that there is a one parameter freedom in selecting an optimized $D$. By exploiting this unnoticed design freedom it became suddenly possible to accurately approximate the T-matrix for much larger particle sizes than it has been till recently deemed possible. As demonstrated on a broad choice of plasmonic materials, involving the traditional (Ag,Au), increasingly popular (Al), and a very recent alternative (Mg) plasmonic metals, the optimized MLWA is shown to yield surprisingly accurate results for plasmonic spheres for a broad range of their radii up to $160$~nm, including higher order multipoles ($\ell>1$). The precision of our optimized MLWA is truly remarkable, while essentially doubling its expected range of validity.

Quantum hydrodynamic theory (QHT) is a powerful method to calculate the optical response of metallic nanoparticles (NPs) since it takes into account nonlocality and spill-out effects. Nevertheless, the absorption spectra of metallic nanoparticles obtained with conventional QHT, i.e., incorporating Thomas-Fermi (TF) and von Weizsäcker (vW) kinetic energy (KE) contributions, can be affected by several spurious resonances at energies higher than the main localized surface plasmon (LSP). These peaks are not present in reference time-dependent density-functional-theory TD-DFT spectra, where, instead, only a broad shoulder exists. Moreover, we show here that these peaks incorrectly reduce the LSP peak intensity and have a strong dependence on the simulation domain size so that a proper calculation of QHT absorption spectra can be problematic. To overcome this issue, we propose to complement QHT with functionals that depend on the Laplacian of the electronic density, thus, beyond the gradient-only dependence of the TFvW functional. By doing this, we obtain the absorption spectrum that is free of spurious peaks, with LSP resonance of correct intensity and numerically stable Bennett state. Finally, we present a novel Laplacian-level KE energy functional that is very accurate for the description of the optical properties of NPs with different sizes as well as for dimers. Thus, the Laplacian-level QHT represents a novel, efficient, and accurate platform to study plasmonic systems.

We provide the first complete electronic and photonic theory of luminescence from Drude metals. We resolve a series of arguments about the basic nature of the emission, its spectral shape and electric field dependence.

On two new optical forces acting on magnetoelectric particles Manuel Nieto-Vesperinas1, Xiaohao Xu2, Cheng-Wei Qiu3 1.Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), Madrid 28049, Spain. 2.Institute of Nanophotonics, Jinan University, Guangzhou 511443, China. 3.Department of Electrical and Computer Engineering, National University of Singapore Singapore 117583, Singapore. We show two new optical forces that we have recently discovered. One derives from a vortex density of azimuthal imaginary Poynting momentum (IPM) which we show to be built by a superposition of radially and azimuthally polarized beams. Further this azimuthal IPM density may exist with a donut beam intensity distribution, and with zero azimuthal component of all other momenta. This discovery is important because while the spin momentum of a light beam loops in circularly polarized beams and the orbital momentum spirals in helically phased beams, such a behavior of the IPM had not yet been found. The resulting novel effect for optical manipulation is the rotation of spherical particles in absence of incident spin and orbital angular momenta. The second force that we address derives from the interference between the electric and magnetic dipoles induced by light in a magnetodielectric particle, (which gives rise to those well-known Kerker interference effects in the angular distribution of scattered intensity), producing an intensity gradient force which, in contrast with the well-known gradient force employed in standard optical tweezers, is either attractive or repulsive, as well as non-conservative on illumination of the object with either linearly or elliptically polarized Gaussian beam. This new force is directionally anisotropic, tending to repel particles away from the beam axis. Such repulsive effects enhance the sensitivity of the optical manipulation configuration to the particle size. On the basis of this behavior, all-optical sorting of Si nanoparticles is theoretically demonstrated, with tunable size-selection criterion and accuracy.

Nanomechanical resonators with ultra-low dissipation constitute the ideal systems for applications ranging from high-precision sensing to quantum transduction between disparate quantum systems. Traditionally, the improvement of the resonator’s performance through nanomechanical engineering such as dissipation dilution and strain engineering has been driven by human intuition and insight. Such an approach is inefficient and leaves aside a plethora of unexplored mechanical designs that potentially achieve better performance. Here, we present a computer-aided approach known as topology optimization to structurally design mechanical resonators with optimal performance of the fundamental mechanical mode. Using this approach we fabricate and characterize new nanomechanical resonators with record-breaking performance of its fundamental mode [1]. In addition, we present another approach based on a novel type of phononic crystal engineering that creates full bandgaps with high quality modes. With this approach, we make nanomechanical resonators with extremely high quality factors. These approaches open up a new paradigm for designing ultra-coherent nanomechanical resonators for cutting-edge technology and applications. [1] Dennis Høj, Fengwen Wang, Wenjun Gao, Ulrich Busk Hoff, Ole Sigmund, Ulrik Lund Andersen, arXiv: 2103.15601

Liquid-core fibers are a versatile platform for nonlinear light-matter interactions, combining highly nonlinear materials like carbon disulfide or nitrobenzene with the confinement and long interaction length of optical fibers. While there is no strain inside the fiber core due to the liquid phase, pressure effects have a more dominant role depending on the thermodynamic regime and filling of the fiber core. We experimentally demonstrate localized and distributed optoacoustic interactions through Brillouin Optical Correlation Domain Analysis (BOCDA). Due to the associated refractive index change, this response is strain, pressure and temperature dependent. The strong and tunable Brillouin response in sealed carbon disulfide-filled liquid-core fibers offers a unique opportunity to study fundamental optoacoustics in liquids and to realize SBS-based applications, such as signal processing and sensing.

Targeted drug delivery is one the main research directions in biophysical investigations with far-going practical applications. Here we will demonstrate our approach to capsules delivery, based on optomechnical tools. The emphasis will be made on optical and optomechanical properties of nanostructured mesoporous vaterite particles and vaterite-based metamaterials.

In this talk I will introduce a novel technique for airborne particle metrology based on hollow-core photonic crystal fiber. It relies on optical forces that automatically capture airborne particles in front of the hollow core and propel them into the fibre. The resulting transmission drop, together with the time-of-flight of the particles passing through the fibre, provide unambiguous mapping of particle size and refractive index with high accuracy. The technique can be directly applied to monitor air pollution in the open atmosphere and precise particle characterization in a local environment.

Phonon polaritons - light coupled to optical lattice vibrations - in 2D materials can exhibit ultra-short wavelengths, long lifetimes and strong field confinement, which allows for manipulating infrared light at the nanometer scale. Here, we demonstrate how they can be utilised to achieve vibrational strong coupling with nanoscale amounts of organic molecules. To that end, we employ far-field spectroscopy and real-space nanoimaging experiments of ultra-confined infrared phonon polariton in hexagonal boron nitride (h-BN) nanostructures and layers that are adjacent to molecule layers.

When the coupling between a confined electromagnetic mode and the electronic degrees of freedom of a solid-state system becomes large enough, the interaction can modify the electronic wavefunctions and the related material properties. These effects become more dramatic in systems with continuum electronic degrees of freedom, in which the gapless spectra enhance the electronic malleability. Solid-state cavity quantum electrodynamics can thus become a tool for quantum material engineering, allowing us to drastically enrich the catalogue of materials available for scientific and technological applications. In this talk I will present the first experimental demonstration of cavity-induced single-photon wavefunction modification in which we measured a change of 30% for the Bohr radius in microcavity embedded quantum wells [1]. Using doped quantum wells characterised by a continuum spectrum we then predicted [2] and demonstrated [3] the formation of novel excitons bound by photon exchange. We also observed related polaritonic nonlocal effects [4] reducing the achievable field enhancement and thus the achievable strength of the light-matter coupling. [1] Experimental verification of the very strong coupling regime in a GaAs quantum well microcavity. S. Brodbeck et al.,Phys. Rev. Lett. 119, 027401 (2017) [2] Strong coupling of ionising transitions.
E. Cortese et al., Optica 6, 354 (2019) [3] Excitons bound by photon exchange.
E. Cortese et al.,
Nature Physics 17, 31 (2021) [4] Polaritonic nonlocality in light-matter interaction.
S. Rajabali et al., Nature Photonics, (2021). doi.org/10.1038/s41566-021-00854-3


The rapid growth of nanofabrication and nanotechnology has enabled the design and realisation of a plethora of new templates for understanding, controlling, and enhancing light—matter interactions. Plasmonic nanoparticles, with their intense near-field enhancements, have been particularly efficient in this task, and reaching the strong coupling regime with quantum emitters has been repeatedly demonstrated. Mie-resonant dielectric nanoparticles, on the other hand, are characterised by lower nonradiative losses, and can often be considered as potential alternatives to plasmonics, but their potential as photonic cavities has been explored much less. Here I will discuss our recent activities on tailoring light—matter interactions with both kinds of architectures as templates. Regarding plasmonic nanostructures, I will focus on the role of quantum corrections in the response of the metal, and show that they open new nonradiative decay channels, which do not, however, prevent the system from entering the strong coupling regime; on the contrary, they can even enable interesting non-Markovian relaxation dynamics in nearby two-level systems. Regarding dielectric nanostructures, I will show, both theoretically and experimentally, that achieving the strong coupling regime is feasible, and discuss the advantages of such environments in terms of emitter position and orientation, and the potential to control the emitter—nanoparticle coupling with external stimuli.

Nanolasers are commonly described within a weak-coupling picture by rate equation models, in which the rates of spontaneous and stimulated emission are given by Fermi's golden rule. However, even when the light-matter coupling constant is small, emitters collectively produce macroscopic polarization, leading to the polaritonic transformation of the cavity mode. At the same time, no hybridization occurs in emitters. Using a fully quantized description of light-matter interaction, we derive the modified Fermi's golden rule, which properly accounts for many-body effects, and obtain compact expressions for radiative rates. These expressions explicitly state that the Purcell enhancement of the spontaneous emission depends on the modal gain provided by emitters while the stimulated emission rate is not bound to the spontaneous emission by Einstein's relations.

Spatial resolution is an important issue at laser action on to a thin films in nanoelectronics and nanophotonics. The report discusses the possibility of implementing resolution within the wavelength. It is based on a strong nonlinear dependence of the growth rate of metal oxides on the temperature in the laser exposure area, along with other nonlinear effects. It is theoretically shown and experimentally confirmed that the sharper an intensity distribution inside the laser spot the higher the thermochemical resolution of the laser image, . Points and lines are implemented for diffractive optical elements up to 70 nm in a size in the laser spot diameter of about 500 nm.

We study active dielectric metasurfaces composed of two-dimensional arrays of split-gap nanodisk resonators fabricated in InGaAs slab with embedded InGaAsP quantum wells. Depending of the geometric parameters, such split-gap nanodisks can support optical anapole states originating from the overlap of the electric dipole and toroidal dipole modes, with strongly localized fields and high-Qresonances. We demonstrate room-temperature lasing from the anapole states of the engineered metasurfaces with high coherence, narrow linewidth, and low threshold.

The dynamics of light in active optical systems with periodic complex potential is considered using coupled modes approach where the field is approximated by two counter propagating waves. It is demonstrated that shifting the position of the imaginary part of the potential (effective gain) with respect to the real part of the potential (variation of the refractive index) one can control the effective gain/losses seen by the upper and the power modes. This effect can be used to control the radiation from the laser. The effect of the Kerr nonlinearity is also considered and it is shown that this can result in spontaneous symmetry breaking leading to the formation of the hybrid nonlinear states.

Recently, the study of halide perovskites has attracted enormous attention due to their exceptional optical and electrical properties. As a result, this family of materials can provide a prospective platform for modern nanophotonics and meta-optics, allowing us to overcome many obstacles associated with the use of conventional semiconductor materials. Here, we overview the recent progress in the field of halide perovskite nano- and microlasers starting from single-particle light-emitting nanoantennas and nanolasers to the large-scale realizations as well as integrated designs.

Currently, halide perovskites are very perspective materials not only for photovoltaics but also for nanophotonic and especially nonlinear optics. These materials have already demonstrated high two-, three- and many- photon absorption coefficients, strong Kerr-nonlinearity, and high-efficient second harmonic generation. Easy and cheap fabrication gives halide perovskites a wide area for scientific research and engineering applications. However, to achieve the stability of perovskites is still a challenging task, which scientific community is working on. In this work, we study a new form of encapsulation of perovskite nanoparticles in sub-micron porous dielectric nanospheres. Due to small pores in such spheres, perovskites are not only protected from external factors, but also are confined in size, which brings several features in the photoluminescence emission. We also show resonant properties of spherical sub-micron particles, which can be used for enhancing upconversion photoluminescence intensity.

In this work, we numerically study the luminescence of nanodiamonds with NV centres embedded in a polymer layer on the surface of one-dimensional photonic crystal. The interaction of NV center spontaneous emission with the Bloch surface wave (BSW) is demonstrated. The presence of a photonic crystal leads to a change in the angular distribution of the emitter radiation due to the coupling of luminescence to BSW. We show that the best coupling efficiency of 71% is observed when NV centres are located in the close proximity to the BSW field maximum.

Proposed originally as a visual alternative to proving theorems in mathematical logic [1], Wang tilings have found applications in computer graphics or biological computing. In this contribution, we discuss the use of Wang tilings to design and optimize architectured non-periodic (meta)materials and structures. The talk splits into three parts. The first part addresses the tiling concept in its most straightforward installment [2], employing a single tile, possibly rotated by 90 degrees, that allows assembling auxetic or non-auxetic structures. In the second part, we show that the elementary scenario naturally extends to the framework of vertex-based Wang tilings and demonstrate its use in the design of a soft porous metamaterial with a non-periodic structure. Here, the emphasis is on the inherent modularity of this concept and its potential for scalable robot-assisted manufacturing. The concluding part of the talk is devoted to developing a two-level optimization tool to simultaneously optimize the geometry of tiles and their placement in the structure. In particular, we focus on the problem of the minimum-compliance design of modular truss structures [3], for which we demonstrate the performance gains and losses relative to uniform and non-modular designs, respectively. Acknowledgment. This work was supported by the Czech Science Foundation project No. 19-26143X. References [1] Wang, H. (1961). Proving theorems by pattern recognition—II. Bell System Technical Journal, 40(1), 1-41. [2] Nežerka, V., et al. (2018). A jigsaw puzzle metamaterial concept. Composite Structures, 202, 1275-1279. [3] Tyburec, M., et al. (2020). Modular-topology optimization with Wang tilings: an application to truss structures. Structural and Multidisciplinary Optimization, https://doi.org/10.1007/s00158-020-02744-8

Pyrolysis of microstructures made by two-photon lithography (TPP) allows to increase the printing resolution and modify their chemical composition at the same time. In this work, we compare the effect of pyrolysis on TPP-made solid objects sized by tenths of micrometers produced from three photoresists: IP-Dip, OrmoComp®, and SZ2080™. We analyzed the structures' size reduction, modification of chemical composition, and adhesion to the silicon wafer substrate for the pyrolysis temperatures of 450°C and 690°C [1]. Fig. 1 shows SEM images of microcube structure with 34×40.2×50 μm3 dimensions made of IP-Dip before and after pyrolysis at 450◦C. As a result of pyrolysis, the microcube shrinks and deforms. However, with adjusted printing parameters and pyrolysis procedure, it is possible to achieve uniform shrinkage and apply pyrolysis as a repeatable post-processing step for TPP-made structures made of IP-Dip, OrmoComp®, and SZ2080™. Using thermogravimetric analysis, scanning electron microscopy, and X-ray energy dispersive analysis, we have detected pyrolysis-induced changes in microstructures' size, chemical composition, survival rate, and adhesion. In conclusion, we have analyzed the effect of pyrolysis on microstructures made of three photoresists for the temperatures of 450◦C and 690◦C. All photoresists have their advantages: pyrolyzed IP-Dip structures have the highest shrinkage ratio of 2.1 at the temperature of 450◦C, OrmoComp® structures demonstrate best adhesion and survival rate after pyrolysis, while SZ2080™ structures are good at decoupling from the substrate's surface and uniform shrinking. The results of the current work can be useful for overcoming the regular TPP restrictions. This work was supported by Russian Science Foundation (20-12-00371), the Ministry of Science and Higher Education of the Russian Federation (14.W03.31.0008), and MSU Quantum Technology Center. M.I. Sharipova, T.G. Baluyan, K.A. Abrashitova, G.E. Kulagin, A.K. Petrov, A.S. Chizhov, T.B. Shatalova, D. Chubich, D.A.Kolymagin, A.G. Vitukhnovsky, V.O. Bessonov, and A.A. Fedyanin, “Effect of pyrolysis on microstructures made of various photoresists by two-photon polymerization: comparative study,” Opt. Mater. Express 11, 371-384 (2021).

We present a platform for the inverse design of flat optics that are robust to fabrication errors and mechanical deformation. Experimentally, we show flexible polarizers that maintain 80% efficiency when curved over a 200 nm bandwidth.

The asymptotic homogenization technique is applied to evaluate the effective properties of thin plates with periodic heterogeneity. The effect of shear deformation in the homogenization process is evidenced and the role of cell slenderness, besides that of the plate, is clarified by several numerical analyses.

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In this work the excitation and amplification of terahertz plasma waves in a structure with two layers of hydrodynamic graphene containing one layer of graphene with a DC-current and one layer of graphene without DC-current is theoretically investigated. The plasmons are excited in the structure under study by the method of attenuated total reflection of the terahertz wave incident on the structure at a random angle.

Ensembles of silver nanoparticles (NPs) with size ~45 nm formed from the silver film using an ion beam modification are studied. The optical spectroscopy demonstrated that the fabricated ensembles of silver NPs keep stable their plasmonic properties in an ambient atmosphere for at least 39 days due to their monocrystalline nature. We use the scanning Raman microscope to map the SERS from Crystal Violet homogeneously adsorbed on these ensembles. It was found that the manufactured ensembles have a strong amplification factor, and this factor is preserved for these ensembles even after more than one month of storage in the surrounding atmosphere. Hereby, by ion beam modification of silver film, it is possible to fabricate the NPs with stable plasmonic properties and form nanostructured surfaces to be applied in sensor technologies and SERS.

Surface-enhanced Raman spectroscopy (SERS) is a potent and highly selective tool to chemically identify and determine the structure of molecules and materials. However, the large biomolecules and living cells are still difficult to study using modern SERS-substrates. Here we present a new approach to the geometry of the surface of plasmon nanostructures (cellular surfaces), which makes it possible to efficiently work with volumetric objects as cells or organelles. We use the scanning Raman microscope to map the SERS from the specially prepared microcapsules formed with a Layer-by-Layer deposition method and with built-in Raman tags (Indocyanine green). It was demonstrated the possibility to detect SERS signal from Indocyanine green in microcapsules located in cavities, while the signal from the Raman dye in microcapsules located on a flat surface is not detected. The obtained results can be useful in biosensors applications.

Optical properties of hyperbolic metamaterials (HMMs) are in stark contrast to properties of ordinary media that fuels interest to various applications of HMMs in photonics. Special attention is attributed to the epsilon-near zero regime (ENZ) of HMMs that is the spectral point in which real part of the permittivity of the HMM becomes zero. This is accompanied by the effects of field enhancement having far-reaching applications. Here we focus on the experimental and theoretical investigation of the propagation of an ultrashort laser pulse through the silver nanorod-based HMM slab in the spectral range over the ENZ. We revealed pronounced resonant change of the pulse delay in HMMs and the transition between the superluminal and slow pulse propagation at the ENZ spectral point. Observed dynamical phenomena are confirmed theoretically and attributed to unusual case when the spectral half of an ultrashort pulse has elliptical dispersion and another has the hyperbolic one. Special attention is payed to the propagation of chirped laser pulses in the HMMs.

Nanophotonics is a rapidly developing branch of physics that studies light interaction with nanoscaled objects such as metamaterials. Hyperbolic metamaterials (HMMs) based on ordered arrays of metal nanorods embedded in a dielectric matrix are of great interest due to their nontrivial optical properties and abilities to control over the parameters of light. In this article, we present the results of nonlinear absorbtion measurements in HMMs based on ordered arrays of silver nanorods. The main finding consists in the spectral vicinity of Epsilon-Near-Zero and Epsilon-Near-Pole features.

In this work, propagating surface plasmons in one-dimensional magnetoplasmonic crystals (MPCs) are studied by aperture type scanning near-field optical microscopy (SNOM). Near-field around the aperture probe is used to locally drive surface plasmons in the MPC. The SNOM signal represents the scattered intensity caused by the interaction of the SNOM probe near-field with the MPC. Scanning of the MPC surface with polarization resolving of the scattered radiation shows decreasing of the intensity due to the surface plasmon excitation. The observed polarization dependence of the scattered SNOM signal is associated with the selective coupling of the near-field components of the SNOM probe with surface plasmons. By means of finite-difference time-domain simulations, the experimental SNOM signal is reproduced and the excitation of surface plasmons with symmetric and antisymmetric field distribution is demonstrated.

Resonant optical properties of the magnetoplasmonic crystals, which support propagation of surface plasmon polaritons (SPPs) accompanied by magnetooptical effects, have found success in magnetic field driven control of optical radiation. In this work we investigate the resonant magnetooptical effects in the second harmonic generation in the magnetoplasmonic crystal formed by gold/pemalloy bifilm covering dielectric grating. Strong transverse magnetooptical Kerr with the contrast up to 30% is revealed in the spectral vicinity of the SPP excitation.

While photons always push an object, the counter-intuitive phenomenon of optical pulling can be achieved in some special cases. However, such pulling can only be achieved for specially structured light beams acting on special particles and typically only operates in a short range close to the light source. We show that long range optical pulling can in principle be achieved using an air waveguide sandwiched between two chiral hyperbolic metamaterials for a particle with arbitrary shape and size and made up of arbitrary material.

The creation of optical forces on dielectric micro-particles were first realized using optical beams. Subsequently, the particle manipulation using light has evolved in several ways, for example, applying it to a broad range of micro-objects (dielectric and metal particles, biological cells, molecules, atoms) and creating sophisticated optical fields for intricate manipulation of the objects. Another direction involves the manipulation of particles near interfaces using either guided waves or incident optical beams. The presence of interfaces serves several purposes. First, it allows using surface waves with large concentration of energy near interfaces. Second, it enables the energy exchange between the particle resonance and the guided mode. Various interaction scenarios and effects related to the appearance of the optical forces on resonant particles near interfaces will be discussed. These effects include the appearance of large propulsion forces due to efficient transformation of the surface-wave momentum to force. Another effect is the appearance of not only the textbook gradient force attracting the particle to the interface but also a repulsive force due to the interaction of the particle with the interface. The interplay of these forces may lead to the appearance of an unusual effect -- stable optical equilibrium induced by the incident evanescent fields alone. Specific conditions for the appearance of such levitation will be analyzed. The theoretical models and numerical techniques required to describe accurately the strong interaction between the particles and guided modes will also be discussed.

Optical tweezers (OTs) have turned out to be a versatile and reliable noncontact tool for 3D manipulation of colloidal micro sized objects, which allows sensing by using only a single upconverting particles (UCPs). However when applied to manipulate 30 nm UCPs, the optical trapping force, which is proportional to the volume of trapped particles, becomes insufficient due to dramatic disturbances caused by Brownian motion, especially at high temperature. In this work, a temperature-responsive polymer Poly(N-isopropylacrylamide) (PNIPAM) was coated on the surface of NaYF4:Yb3+, Er3+ UCPs with diameter of 30 nm by using ligand exchange strategy to obtain novel nanocomposite UCP@PNIPAM. This surface coating treatment can not only increase the optical trapping force to achieve stable optically trapping of 30 nm-UCPs at higher temperatures but also introduce temperature-driven volume phase transition, which would result in an increase in the thermal sensitivity of UCPs as sensor. As expected, the optical trapping force exerted on UCP@PNIPAM was enhanced by about 20 times compared to that on core UCP. And UCP@PNIPAM can be optically trapped by 980 nm laser in the temperature range of 20 C to 45C. The optical trapping stiffness and emission intensity of single UCP@PNIPAM trapped and excited by 980 nm laser as function of temperature were also studied. It is shown that near the volume phase transition temperature, trapping stiffness decreases gradually while emission intensity increases upon increasing temperature, which indicates that this kind of stimuli-responsive particles (UCP@PNIPAMs) has a promising application prospect in thermal sensing.

Optical cooling is a process present in rare-earth doped crystals, consisting on an anti-Stokes laser-induced emission in which the rare-earth ions absorb optical-phonons from the host crystal lattice. [1-3] We present a NaYF4:Yb3+ birefringent microdisk dispersed in heavy water. When optically trapped with a 1020 nm laser beam, the Yb3+ ions are excited, inducing optical cooling. If the laser is circularly polarized, the microcooler’s rotation is induced [4,5], which depends on the medium viscosity and consequently on its temperature. A variation in rotation dynamics indicate the relative temperature decrease in the surrounding medium. We observed that a spinning microparticle doped with Yb3+ ions can be used to decrease 6 ºC the temperature of a medium in a non-invasive way, by means of the optical trapping technique. This is the first approach of this type of experiments in a liquid medium and can be the first step for its application as a micro-cooler in local and controlled thermal treatments.

Bloch surface waves (BSWs) are propagating modes supported by all-dielectric multilayer structures with the energy concentrated at the surface. The field of these modes penetrates into the surrounding medium, which makes it possible to use them for optical manipulation of micro- and nanoparticles. In this talk, I will review our experimental studies of optical forces induced by BSWs in dielectric multilayers and discuss their potential for optomechanical applications. We started with a single polystyrene microparticle in water and showed that it can be trapped in the BSW evanescent field and propelled in the direction of the BSW propagation. The forces acting on such a particle were measured using photonic force microscopy. Then, we replaced single microbeads with a concentrated suspension of 50-nm dielectric particles. This made it possible to observe nonlinear self-action of BSWs governed by the optically induced spatial redistribution of particles. Finally, we explore the possibility of tailoring the BSW field using prefabricated dielectric structures on the surface of the multilayers. This could make BSWs a promising platform suitable for trapping, sorting, and transport of particles in microfluidic environment.

Focused laser beams allow controlling mechanical motion of objects and can serve as a tool for assembling complex micro and nano structures in space. Introduction of additional degrees of freedom into optomechanical manipulation suggests approaching new capabilities. Here we analyze optical forces acting on a high refractive index silicon sphere in a focused Gaussian beam and reveal new regimes of particle’s anti-trapping. Multipolar analysis allows separating an optical force into interception and recoil components, in particular, interplaying interception radial forces and multipolar resonances within a particle can lead to either trapping or anti-trapping scenarios and also introduce bending trajectories, depending on the overall system parameters. Multipolar engineering of optical forces paves a way to new possibilities in microfluidic applications, including sorting and micro assembly of nontrivial volumetric geometries.

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We theoretically study the mechanism of photobleaching suppression in the system of molecules strongly coupled with plasmonic nanostructure. We show that strong coupling by itslef can result in increasing of the molecular stability time by the order of magnitude. We show that there is an optimal value of red detuning between plasmon resonance frequency and the transition frequency of molecule for which the photobleaching suppression reaches maximal value. We find this optimal value at different Rabi frequencies. The obtained results pave the way for control of chemical reaction in the vicinity of plasmonic structure.

We examine composite nanospheres of core-shell morphology, consisting of a gyroelectric and an excitonic layer subjected to a static magnetic field. The Mie-exciton modes emerging from the plane-wave excitation of the nanosphere, in addition to a wide range of optical properties, attain intriguing magnetic properties with the introduction of the magnetic field . In particular we reveal the emergence of the photonic Hall effect ---a light component scattered transversely to both the propagation of the incident plane wave and the magnetic field direction--- and show that strong coupling is manifested through the splitting of the primary magnetic dipolar mode into two narrow bands in the scattering cross section spectrum of the magneto-transverse light component. Finally, we discuss the extension of gyroelectric-excitonic structures for nanomedical applications. Biocompatible organic dyes, mimicked by the excitonic material in our study, are already being used in photothermal therapy. A key element of both light and magnetism lies in their ability to function as external stimuli without perturbing the biological system. Appropriately designed nanoparticles, flexible in responding to both, constitute fertile building blocks for non-invasive clinical applications.

Flat optics based on metasurfaces holds promise for the design of a new class of diffractive optical component that circumvents the limits of refractive as well as Fresnel optics, in terms of control of aberrations, compactness and multifunctionality. Here we highlight the enhanced functions enabled by metasurface flat optics in structuring light

Spherical particles both dielectric and metallic are essential building blocks in nanophotonics. During recent rapid development of Mie-tronic — nanophotonics devices heavily using various features of the Mie-resonances — the deep fundamental investigation of the eigen modes of such particles by using the novel tools is still relevant and currently important. Moreover, eigen modes of a sphere are closely related to the Vector Spherical Harmonics which are widely used in the multipolar decomposition to analyze less symmetric structures. In this work we study in details the canonical spin and angular momenta (AM), helicity and other properties of the eigen modes of dielectric (nondispersive) and metallic (dispersive) spheres. We show that canonical momentum density of the AM as quantized and has a close relation to the quantum picture of a single photon. Our work provides a solid platform for future studies and applications of the AM transfer from near fields of spherical particles to the matter in its vicinity.

Periodic photonic nano- and microstructures are routinely used for light manipulation at the nanoscale. However, their fabrication process is demanding in terms of time, cost and facilities. Here we demonstrate a rapid laser-assisted method for fabrication of gratings in Ge2Sb2Te5 (GST) thin films, based on the formation of laser induced periodic surface structures (LIPSS). LIPSS formation mechanisms dependent on the wavelength of the operating laser, lead to high flexibility of the process, producing gratings with tunable period and orientation with respect to the initial laser polarization. The phase-change properties of GST, on the other hand, allows to fabricate phase gratings with strong modulation of refractive index, which are rewritable in nature.

In this work, we show the first experimental observation of accidental bound state in the continuum (BIC) in a periodic chain of ceramic disks. Both in experiment and theory, the linear growth of the radiative quality factor of the BIC with the number of disks is demonstrated. We estimated the number of disks in chain for which the radiation losses become negligible in comparison with the material absorption.

At the moment, planar periodic structures such as metasurfaces and photonic crystal slabs attract particular attention, since they can support surface waves and guided modes with unusual dispersion properties designed on-demand. Once the sample is fabricated, the measured dependence of both propagation constant and propagation length on the wavelength is of great importance. In this work, we propose an experimental approach allowing to retrieve the full complex dispersion of evanescent waves lying deeply beneath the light line, in arbitrary planar structures. The method is based on back focal plane microspectroscopy combined with a solid immersion lens separated from the sample by a precisely controlled nanoscale air gap. Varying the gap between the prism and the sample allows for extracting spectral dependence of both real and imaginary parts of the wavenumber of surface waves propagating in arbitrary in-plane direction. Our approach can be implemented for the development of various on-chip nanophotonic devices.

Ultra-confined optical modes are pivotal ingredients in emerging nanophotonics applications ranging from sensing and light harvesting to signal processing and photochemistry. Such modes grant us the appealing possibility of concentrating light down to atomic-scale regions and enhancing the optical intensity by several orders of magnitude with respect to the externally incident radiation. However, the large mismatch between the spatial extension of ultra-confined modes and the light wavelength is severely limiting the light-mode coupling, which commonly becomes just a small fraction in the incident photons. In this presentation, we will discuss general strategies to increase light-confined mode coupling to near-unity levels, and even reaching 100% in lossless resonant systems. We will also discuss the prospects for potential applications in both classical and quantum optics regimes. References: [1] E. J. C. Dias and F. J. García de Abajo, ACS Nano 13, 5184-5197 (2019) [2] E. J. C. Dias and F. J. García de Abajo, Optica 8, 520-531 (2021)

Classical and quantum photonics with superior properties can be implemented in a variety of old (silicon, silicon nitride) and new (silicon carbide, diamond) photonic materials by combining state of the art optimization and machine learning techniques (photonics inverse design) with new fabrication approaches. In addition to making photonics more robust to errors in fabrication and temperature, more compact, and more efficient, this approach is also crucial for enabling new photonics applications, such as on chip laser driven particle accelerators.

The development of time-resolved Cathodoluminescence (TR-CL) in a scanning electron microscope enabled the measurement of the lifetime of excited states in semiconductors with a sub-wavelength spatial resolution. It was used for example to measure the influence of stacking faults on the GaN exciton 1, to probe the role of a silver layer on the dynamics of a YAG crystal 2 or to show the influence of stress on the optical properties of ZnO nanowires 3. These results demonstrate that TR-CL is essential to study the correlation between semiconductor optical and structural properties (composition, defects, strain…). While all these pioneering studies were done using a scanning electron microscope, the improvement of the spatial resolution and the combination with other electron-based spectroscopies offered by transmission electron microscopes will be a step forward for TR-CL. In this presentation, we will discuss the first time-resolved cathodoluminescence experiments within a transmission electron microscope. They were performed in a unique microscope, based on a cold-FEG electron gun 5. This technology allows among other things to reach a spatial resolution of a few nanometres, essential for the study of III-V heterostructures. After presenting preliminary results on emission centers in nanodiamonds, we will discuss the unique features and opportunities for improvement of this technique.

In comparison to electrons at kinetic energies for transmission electron microscopy, low-energy electrons in the range from 10 to 1000 eV lead to stronger electric fields since their charge is moving slowly through space. The inverse scaling of the electric field amplitude with electron energy enables the efficient excitation of plasmons at nanostructures and strong coupling to quantum systems, opening up new opportunities for fundamental studies of light-matter interaction. In the reverse perspective, plasmonic near-fields from nanostructures can efficiently manipulate the electron beam [1]. Here we combine laser-triggered nanotips – highly coherent point-like sources of low-energy electron pulses [2,3] – with point-projection microscopy and inline holography [4,5] to investigate the interaction of slow electrons with plasmonic fields. In our ultrafast pump-probe study, femtosecond electron pulses interact with fields at a plasmonic nanostructure on a sub-optical-cycle scale, leading to distortion effects in the image of the electron beam. Our predictions and initial experimental evidence demonstrate the feasibility of probing plasmonic fields with nanometer and femtosecond resolution by decoding these distortion effects. [1] N. Talebi, Phys. Rev. Lett. 125, 080401 (2020). [2] M. Krüger et al., Nature 475, 78 (2011). [3] D. Ehberger et al., Phys. Rev. Lett. 114, 227601 (2015). [4] H.-W. Fink, W. Stocker, and H. Schmid, Phys. Rev. Lett. 65, 1204 (1990). [5] J. Vogelsang et al., ACS Photonics 5, 3584 (2018).

Electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDX) are two broadly used techniques in transmission electron microscopy which are sensitive to the chemical composition of the investigated materials. Both measurement techniques share the fact that excitations of atomic states are involved. Indeed, for every X-ray emitted there was at least one electron that gave part of its energy to excite the atom in the first place, and therefore one could imagine that they convey very similar information. However, current EDX detectors have a relatively low energy resolution (100 eV) where for EELS energy resolutions of 1eV are easily accessible. On the other hand, EELS suffers from a large background signal making it hard to detect low concentration elements. Since the two signals originate from the same process, the information on the time-of-arrival of both electrons and x-rays can be exploited in order to select only electrons and X-rays coming from the same process hence significantly reducing the background signal. In the present work, we demonstrate the capability of detecting the single electron events with a time resolution of 1.6 ns by using a Timepix3 detector, which was placed at the end of a spectrometer. The single x-ray detection was performed using a Super-X-EDX detector setup where a digital pulse processor was used to detect the time-of-arrival and energy. This setup shows the potential to improve the signal-to-background ratio of the EEL spectrum and revealing the inelastic scattered electrons coming from low abundance elements in a matrix of majority elements.

In the previous two decades, important technological advancements have expanded the range of temporal resolution in transmission electron microscopes (TEM). Commercial direct-counting and single-electron detectors have revealed dynamics in the ms-timescale. Laser-actuated photoemission microscopes combined with beam scanning, spatially-parsed large area detectors, and sparse-sensing algorithms, can now unlock phenomena at the us to sub-ps timescales. Further optimization of the photoemission stage and beam bunching technologies could potentially extend the temporal resolution into the deep fs-regime. The laser-actuated photoemission microscope however, almost always required new instrument and detector purchases or drastic microscope modifications, in addition to expertise in laser. In practice, this level of investment places time-domain electron microscopy beyond the reach for most research groups. Following our 2016 concept paper, I will be presenting modest modifications to a pair of commercial instruments – one 200 keV Schottky emitter and one 300 keV thermionic emitter, that can confer temporal information spanning the ns and ps range with MHz to GHz repetition rates, in the stroboscopic mode without an excitation laser. The key enabling technology is a pair of broadband phase-matched modulating and demodulating RF pulsers. We have demonstrated 11 ps and 30 ps on the 200 keV and 300 keV microscopes respectively. The placement of the pulsers, mounted immediately below the gun, allows for the preservation of all optical configurations otherwise available to the unmodified instrument, and therefore makes these instruments dual-mode, both stroboscopic time-resolved (strobe) and conventional continuous waveform (CW) capable. In the stroboscopic mode, we recently demonstrated direct visualization of electromagnetic waves moving through a MEMS device [9]. In addition to its time-resolving capabilities, this technology is showing promise for beam damage reduction in soft matter and biomaterials by gating the electrons arriving at the sample [10]. This award-winning (2019 R&D 100 Award, 2020 Microscopy Today Innovation Awards) innovative approach to modifying in-service microscopes has already begun to alter the landscape of ultrafast electron microscopy and has the potential to greatly reduce the access barrier to nanoscale time- and frequency-domain physics.

The interaction between light and electrons can be exploited for generating radiation, such as in synchrotrons and FEL, or for controlling electron beams for dynamical investigation of materials. Using electromagnetic fields, the coherent control of an electron wave function can be pushed to unexplored timescales, enabling new applications in light-assisted quantum devices and diagnostics at extremely small timescales. In this contribution, I will describe an innovative method for coherent longitudinal and transverse phase manipulation of a free-electron wave function. Using appropriately synthesized light fields I will demonstrate how to modulate the energy, linear momentum and orbital angular momentum (vorticity) of the electron wave function with sub-fs precision [1-3]. The experiments have been performed in an ultrafast-TEM, where a relativistic pulsed electron beam was made to interact with properly shaped near-field. The energy-momentum exchange resulting from such interaction was directly mapped via momentum-resolved ultrafast electron energy-loss spectroscopy. Our approach for longitudinal and transverse electron phase modulation at the sub-fs timescale would pave the way to achieve unprecedented insights into non-equilibrium phenomena in advanced quantum materials [4], playing a decisive role in the rational design and engineering of future photonics and electronics applications [5]. [1] G. M. Vanacore et al., Nature Communication 9, 2694 (2018). [2] G. M. Vanacore et al., Nature Materials 18, 573-579 (2019). [3] I. Madan*, G. M. Vanacore* et al., Science Advances 5, eaav8358 (2019). [4] I. Madan*, G. M. Vanacore* et al., Appl. Phys. Lett. 116, 230502 (2020). [5] G. M. Vanacore et al., La Rivista del Nuovo Cimento 43, 567–597(2020).

Discovering unconventional optical designs via machine-learning promises to advance on-chip circuitry, imaging, sensing, energy, and quantum information technology. In this talk, photonic design approaches and emerging material platforms will be discussed showcasting machine-learning-assisted topology optimization for optical metasurface designs for applications in thermophotovoltaics, reflective optics and more.

In optical refrigeration, laser light is used to cool various materials, from dielectrics to semiconductors. Generally, an optical excitation red detuned with respect to the main electronic transition gets unconverted through the process of spontaneous emission, thus carrying energy out of the material via annihilated lattice phonons. I will review progress in cryogenic optical refrigeration of rare-earth-doped dielectrics and focus on the promise of laser cooling in semiconductors. I will conclude by showing a recent demonstration of the cooling of a GaAs semiconductor on sub-nanosecond timescales and review recent claims of steady-state cooling in perovskite nanocrystals.

In recent years, resonant metamaterial perfect absorbers have attracted a great interest in the field of photonics due to their versatile ability in achieving near-unity absorption and in controlling the resonant bandwidth as well as tunability. Among them, infrared (IR) plasmonic metasurface absorbers have found impressive practical applications involving wavelength selective thermal emitter, radiative cooling, and thermal sensors. In this report, we emphasize our recent contributions in developing on-chip narrowband wavelength selective IR sensors utilizing the efficient light-to-heat conversion in a metasurface absorber platform. We successfully demonstrate on-chip MEMS-based quad-wavelength bolometers and ultra-narrowband pyroelectric sensors. The sensor platform presented in this report reveals a clear vison that multi-wavelength spectroscopic device can be fabricated on a single chip using CMOS-compatible MEMS design and can be easily extended into multi-color IR devices.

Near-field radiative heat transfer (NFRHT) exhibits various effects, such as amplification due to the geometry of the system. Recently, NFRHT between two particles in the presence of one or two plates has received focus. It was reported that assistance of surface wave propagation causes a significant amplification of RHT at distances ranging from near to far field. Most recently, we have focused on NFRHT researches on this structure from three aspects. Firstly, we have proposed a theory model for the NFRHT between two nanoparticles in the presence of an anisotropic metasurface. We show that the NFRHT between two nanoparticles are significantly amplified when they are placed in the proximity of an array of graphene strips, and regulated over several orders of magnitude. The dependence of conductance between two nanoparticles on the orientation, the structure parameters, the chemical potential of the GS, and the interparticle or the particle-surface distances are analyzed. These results create a way to explore the anisotropic optical properties of the metasurface based on the measured heat transfer properties. Secondly, we place the two nanoparticles on each side of a periodic layered structure. We show that the resulting heat transfer with the assistance of a multilayered structure is more than five orders of magnitude higher than that in the absence of the multilayered structure at the same interparticle distance. This increase is observed over a broad range of distances ranging from near to far field which is due to the fact that the intermediate multilayered structure supports hyperbolic phonon polaritons, where the edge frequencies of the type-I and type-II reststrahlen bands coincide at a value that is approximately equal to the nanoparticle resonance. This allows high-k evanescent modes to resonate with the nanoparticles. These results illustrate a powerful method for regulating energy transport in particle systems and can be relevant for effective energy management at nano-micro scales. Finally, by employing a drift-biased suspended graphene sheet below the two nanoparticles, we have proposed a newly three-body thermal diode. Nonreciprocal graphene plasmons are induced by the drift currents in the graphene sheet, and then couple to the waves emitted by the particles in near-field regime. Based on the asymmetry with respect to their propagation direction of graphene plasmons, the thermal rectification between the two particles is observed. The performance of the radiative thermal diode can be actively adjusted through tuning the chemical potential or changing the drift currents in the graphene sheet. With a large drift velocity and a small chemical potential, a perfect radiative thermal diode with a rectification coefficient extremely approaching 1 can be achieved within a wide range of interparticle distance from near to far field. This technology could find broad applications in the field of thermal management at nanoscale.

Ultrafast modulation of optical response is realized in a multi-resonant magnetoplasmonic metasurface under resonant femtosecond pump. The sub-picosecond decay is longer for dielectric quasi-waveguide mode than in localized plasmon resonance. A saturation of resonant probe transient transmission is shown at dielectric quazi-waveguide mode. The saturation effect fades out with electron-phonon relaxation. The differential transmittance for the localized nanosphere plasmon modes shows linear behavior for the same pump fluence range.

We study the electrically driven reduction of the optical switching threshold of VO2 based metasurface to optically locally or globally manipulate a wavefront of the transient sub-THz/THz beam. The switching of THz/mid IR/near IR transmission, electric and structural properties induced by direct heating, laser light and electric current are carefully examined. A demonstrated proof-of-concept experiment to reduce an optical switching threshold of VO2 metasurface elements for 10^5 times opens up the way to dynamically program reflective sub-THz metasurfaces using UV/visible/nearIR light pattern.

Owing to its excellent isolation from the thermal environment, an optically levitated silica nanoparticle in ultra-high vacuum has been proposed to observe quantum behavior of massive objects at room temperature, with applications ranging from sensing to testing fundamental physics. As a first step towards quantum state preparation of the nanoparticle motion, both cavity and feedback cooling methods have been used to attempt cooling to its motional ground state, albeit with many technical difficulties. We have recently developed a new experimental interface, which combines stable (and arbitrary) trapping potentials of optical tweezers with the cooling performance of optical cavities, and demonstrated operation at desired experimental conditions. In addition, we implement a novel optomechanical scheme in cavity levitated optomechanics – cavity cooling by coherent scattering – which we employ to demonstrate ground state cooling of the nanoparticle motion. In this talk I will present our experimental result on motional ground state cooling of a levitated nanoparticle and discuss creation of macroscopic quantum states.

Optical control of mechanical motion of solid-state objects weakly interacting with environment, referred to as optomechanics, continues to enable new, ground-breaking methods and applications in the area of ultra-weak force sensing and quantum technologies. The platform based on optically levitated nanoparticles in vacuum (referred to as levitated optomechanics) constitutes an entirely new type of light-matter interface, which provides a broad and an easy tunability of all the system parameters. However, the majority of the previously reported experimental achievements in this area have only dealt with a single levitated object. Here we demonstrate for the first time scalability of the levitated optomechanics to systems containing up to tens of nanoparticles and provide a unique methodology for characterizing the system parameters and non-linear inter-particle interactions. This work represents the first and crucial step in accessing many-body dynamical effects in the classical and quantum regimes. In particular, it opens the door to the experimental studies of many-body stochastic thermodynamics and to the preparation of mesoscopic entangled states between relatively massive objects.

In this talk we face the challenge of measuring the temperature dependence of the velocity of a single colloidal nanoparticle towards full understanding of the fundamentals governing its dynamics. Knowledge of instantaneous velocity allows to distinguish between ballistic and diffusivity regimes and to evaluate the complex nanoparticle-medium interaction. Despite its interest, the experimental determination of instantaneous velocity of nanoparrticles remains unachieved and only room temperature experiments have been performed up to now. Here we demonstrate how is possible to assess to dtermine the temperature dependence of the instantaneous velocity of a nanoparticleby measuring the optical forces acting on a single upconverting nanoparticle at different temperatures. A straightforward analysis of our experimental data allows us to determine the temperature dependence of the diffusive velocity of a single colloidal upconverting nanoparticle. Not only that, comparison with theoretical predictions highlighted an unexpected increment of nanoparticle mobility at high ( ≳ 40 ⁰C) temperatures. This has been correlated with the anomalous temperature dependence of water properties at such high temperatures that leads to a reduction in the dynamic viscosity experienced by the upconverting nanoparticle.

Colloidal self-assembly has been investigated as a promising approach for the fabrication of photonic materials and devices to make, e.g., coatings, displays, and sensors for diagnostics. The final optical properties of such materials strongly depend on the interactions among the constituent colloids and on their reciprocal spatial arrangement. Photonic crystals of periodically arranged colloids for instance are optical materials that can manipulate the flow of light through controlled interference, while randomly distributed colloids can be employed to fabricate robust lasing systems where laser action is obtained thanks to the multiple scattering of light within the material. In this talk, I will show how controllable interactions in light-activated colloids can trigger the reversible assembly of dynamic soft materials for applications in photonics.

Conventional metamaterials and metasurfaces are artificially engineered structures realized by arranging suitably designed sub-wavelength inclusions in a host medium. A variety of advanced field manipulations can be attained by gradually changing the inclusions’ properties along one or multiple spatial directions. More recently, the increased availability of rapidly reconfigurable inclusions has granted access to the temporal dimension as well, and the field of space-time meta-structures is establishing itself as one of the most promising research areas. In a series of ongoing studies, we have been exploring a class of space-time metastructures based on the concept of “digital coding metasurface”. These platforms rely on a limited number of (e.g., only two) inclusion types, which not only yields significant simplifications in the design process, but also establishes an important connection between the physical and digital worlds, with fascinating information-theoretic implications and perspectives. Moreover, the “coding” description of metamaterials is particularly apt to the integration of active elements (e.g., diodes or micro-electro-mechanical systems) controlled by an integrated circuit, thereby leading to “programmable” metamaterial architectures. The temporal dimensionality represents a crucial addition within the emerging paradigm of “information metastructures”, enabling advanced field-manipulation capabilities in both the frequency and spatial domains. Examples include harmonic beam steering and/or shaping and programmable nonreciprocal effects. Potential applications are abundant, and include for instance multi-input and multi-output wireless communications, cognitive radars, adaptive beamforming, and holographic imaging. This talk will provide a compact summary of the main outcomes from our studies, as well as possible future investigations and perspectives.

Temporal modulation is an additional degree of freedom for engineering electromagnetic systems, which opens up novel possibilities, results in exceeding conventional limitations and allows us to design efficient systems with various functionalities. Recently, we have made some steps to fundamentally understand the basics and principles underlying this re-emerging research area. In particular, our efforts have been mainly directed towards studying time-varying lumped elements and scattering from time-varying subwavelength particles. Regarding the first direction, we have focused on studying time-varying resistances, capacitances, and inductances, and on investigating the possibilities that can be provided by temporally modulating these components (such as extreme accumulation of electromagnetic energy). About the second direction, we have attempted to initially describe a meta-atom that is modulated in time, and, subsequently, scrutinize the instantaneous radiation effects and the polarizability of such time-varying meta-atoms. In this invited talk, we review all these efforts that we have done in these few years, and, also, explain our current activities and future plans in this area.

In this contribution we present the most recent results from our group about the opportunities offered by time-varying metamaterials and metasurfaces for conceiving antenna systems and devices exhibiting artificial non-reciprocity, frequency conversion, energy accumulation and temporal electromagnetic scattering. Such artificial metastructures are characterized by constitutive parameters (permittivity, permeability and/or surface impedance) that are modulated in time through an external control or requires modulated excitation signal for enabling anomalous scattering behavior. Here, we briefly describe the physical insights of the unusual interaction arising between the electromagnetic field and such metamaterials and metasurfaces, and then we present some antennas and propagation applications, showing the performances of non-reciprocal antenna systems, magnet-less isolators, Doppler cloaks, temporal devices and metasurface-based virtual absorbers.

Electronically steerable antennas, that are compact, thin, light and contain no mechanical parts, are being more and more used for satcom applications notably owing to the fast development of mega constellations and 5G with the arrival of mmWave; yet current designs still have many limitations. Indeed, all designs up to date rely on the same old concept, phased arrays, namely, large number of sources that are phased matched to point in various directions. These can be passive, in the sense that a common feed is used to radiate through many radiators, or active in which case each tiny emitter contains its own source of waves. While the former are relatively simpler and less energy greedy, they are very dissipative and hence of poor efficiency. The latter, on the contrary, often offer good performances, yet they are extremely costly and require huge amounts of electrical power to operate, the vast majority of which is dissipated into heat. In a nutshell, both active and passive phased arrays have tremendous problems that need to be overcome before they are vastly used. Here we introduce the concept of leaky reconfigurable cavity antenna, that stems on a radically dif-ferent approach to beamforming. It uses a thin leaky cavity that, when excited by one or several feeds, can establish any desired wavefield corresponding to any desired radiation pattern. To achieve this, the cavity is reconfigured in real time by an electronically reconfigurable metasurface. The latter con-trols the reflections of the waves inside the cavity, acting as a software-controlled set of boundary conditions. Being based on discrete components, the antenna maintains the cost-efficiency, robust-ness and power sobriety of the simplest passive phased arrays, with a power needed for beamforming as low as a few tens of watts at Ku or Ka. Furthermore, since the control is solely based on electron-ics, it achieves the performances of active phased arrays at the same time, for instance in terms of gain or switching speeds. With its high performances and low complexity, our concept paves the way to the deployment of electronically steerable antennas at scale. Further, since the beamforming does not result from the synchronization of many elementary sources, but rather on the shaping of a wavefield inside a cavity, our concept is standard or protocol agnostic. Moreover, it is able to support multiple frequency bands, and to emit multiple beams, at different frequencies, with different polarizations and an optimal scan loss.

In this talk, I will demonstrate that a chaotic enclosure with boundary conditions tuned by programmable meta-atoms enable coherent perfect absorption (CPA) at any desired frequency. CPA is an exotic scattering phenomenon corresponding to a zero of the scattering matrix lying on the real frequency axis so that an incoming wavefront is perfectly absorbed within the enclosure. I will then show that the sharp dip of the energy reflected off the system at CPA condition is associated with a divergence of the time-delay which can be positive or negative. Our experimental results are fully confirmed with a theoretical model based on an effective Hamiltonian and corroborated with random matrix simulations. The divergence of the time-delay provides optimal sensitivity to detect minute perturbations so that our study paves the way for sensors with optimal sensitivity. Finally, I will show that if the impinging wavefront cannot be shaped, doping a medium with programmable meta-atoms even enables to adapt the random medium to any arbitrary wavefront.

The perfect-absorption (PA) scattering anomaly (a real-valued scattering matrix zero) requires balanced excitation and decay rates, which can be achieved in carefully engineered systems like metasurfaces but virtually never occurs in random scattering media. We identify a route toward observing real-valued zeros in complex scattering systems that relies on doping the latter with meta-atoms whose scattering properties can be reprogrammed in situ to purposefully tune the medium’s scattering matrix. We demonstrate our idea in a 3D microwave chaotic cavity excited by a single channel and equipped with an array of one-bit reflection-programmable meta-atoms. In contast to recent reports on observing PA in complex media by scanning a wide parameter space involving operation frequency and attenuation in the system (which was limited to originating from a single localized loss center), our approach offers on-demand access to PA at an arbitrary frequency and attenuation level. Our principle can be straight-forwardly generalized to multi-channel excitation and the need for coherent wave control in that case can be circumvented by imposing appropriate additional optimization constraints. The extreme sensitivity of the PA condition to any sort of perturbation can be related to the divergence of the time delay and offers enticing applications in wave filtering, precision sensing and secure communication. We experimentally prototype a physically secure backscatter wireless communication scheme based on the proposed PA technique.

We provide proof of concept demonstrations of halide perovskite light emitting metadevices, like a phase-change tunable vortex laser with optical bistability and chiral emitting metasurfaces with high degree of circular polarization. Halide perovskite are emerging as a new material platform for all-dielectric metasurfaces. In addition to the high refractive index, they offer unique charge transport and luminescence properties which can be exploited for the realization of active metadevices, in which light emission is controlled by structural design and external stimuli. Here we provide proof of concept demonstrations of a methyl-ammonium lead iodide (MAPbI3) based phase-change tunable vortex laser with optical bistability and a chiral emitting metasurface with high degree of circular polarization: i) the design of the vortex laser is based on an all-dielectric metasurface that supports bound states in the continuum (BIC) with opposite topological charges, which provides bistable spectral and modal tunability when the perovskite undergoes a temperature-induced structural phase transition; ii) the design of the chiral emitting metasurface is based on in-plane inversion symmetry breaking that generates circular polarized virtual optical states of opposite chirality. The active control of light-emitting parameters (e.g. wavelength, polarization, spatial mode distribution) in designer metasurfaces, combined with the synthetic flexibility of perovskites, paves the way for a new class of reconfigurable nanophotonic devices for the visible to NIR range.

Nonlinear and electro-optic devices are widespread as light sources for microsurgery, green laser pointers, or modulators for telecommunication. Most of them use bulk materials such as glass fibres or high-quality crystals, hardly integrable or scalable due to low signal and difficult fabrication. Generating nonlinear or electro-optic effects from materials at the nanoscale can expand the applications. However, the efficiency of nanostructures is low due to their small volumes. Here, we show several strategies to enhance optical signals by engineering metal-oxides at the nanoscale with the goal of developing nonlinear and electro-optic photonics devices for a broad spectral range and over large surface area. Metallic and semiconductor nanostructures as gold or gallium arsenide are limited to the visible to near infrared range by their high absorption. We use metal-oxides such as barium titanate (BTO) and lithium niobate (LNO) as an alternative platform for nanoscale nonlinear photonics in a broad spectral range. Both BTO and LNO are non centrosymmetric materials with high refractive index and high energy band gaps, transparent down to the near-ultraviolet range. We already demonstrated linear Mie resonances in BTO and LNO nanostructures, such as nanospheres or nanocubes. Further, we showed that these resonances enhance the second-harmonic generation emission from the nanostructures. Recently, we focused on bottom-up assemblies of barium titanate nanoparticles to obtain electro-optic metasurfaces or random quasi phase matching effects. We show an electro-optic response in assembled nanostructures as strong as certain other perfect crystalline structure.

In this work we develop the concept of integrated light source based on halide perovskite microlasers for Bloch surface waves (BSWs) in one-dimensional photonic crystals. We theoretically study modes supported by a CsPbBr$_3$ microwire placed on the surface of a photonic crystal. The modes with field distribution similar to BSW are observed. We study the coupling of microwire modes with BSWs depending on the geometric parameters of the wire. BSW excitation efficiency exceeding 40\% is found for BSW-like modes of microwire. The perovskite radiation coupling with BSWs is experimentally studied by leakage radiation spectroscopy method. Our research paves the way for the implementation of complete integrated optical setups on the surface of photonic crystals.

Over the past two decades, nanosized diamond particles with various luminescent defects have found numerous applications in many areas from quantum technologies to medical science. The size and shape of diamond particles can affect drastically the luminescence of embedded color centers. Here we study diamond particles of 250–450 nm in size containing silicon-vacancy (SiV) centers. Using dark-field scattering spectroscopy, we found that fundamental Mie resonances are excited in the spectral range of interest. We then measured the fluorescence saturation curves under continuous excitation to estimate the effects of the excitation and Purcell factor enhancement on the luminescent properties of the studied particles. The results show that the saturation excitation intensity differs by several times for particles of different sizes which is well explained by the numerical model that takes into account both the Parcell factor enhancement and resonant excitation.

We analyze the TE-TM polarization degeneracy of the guided modes of dielectric metasurface in the microwave frequency range. We find the optimum metasurface design and investigate the dependence of the degeneracy degree on the propagation direction. Finally, we simulate the possible microwave experiment demonstrating the polarization-degenerate spectrum in all propagation directions. The results obtained could be useful for polarization flat photonic devices.

In the recent years, all-dielectric nanophotonics has been showing promising potential for biotechnology, with important progress in the development of efficient all-optical, all-dielectric nanosensing devices overcoming the ohmic losses inherently present in their plasmonic counterparts. In the quest to achieve single molecule sensitivities, a judicious design of the optical response of the nanoantennas is required. Here, we approach this problem from the perspective of non-Hermitian physics and investigate the interaction of two finite nanorods supporting Mie resonances, with the aim of maximizing the frequency detuning induced by a perturbation of the structure. We develop a simple semi-analytical technique to efficiently investigate the coupled system, and we find that Coulomb interactions, together with mutual interference induced by breaking the dimer symmetry, can effectively bring the structure towards a non-Hermitian singularity, an exceptional point, that can potentially increase the sensitivity. The results of this work are expected to lead to novel developments in all-optical single molecule detection, and merge for the first time all-dielectric nanophotonics with exceptional point physics.

Parity-time (PT) symmetry is a condition that allows non-Hermitian systems to have real eigenfrequencies. At exceptional points these frequencies degenerate into one, and so do the corresponding states. In optical systems, PT-symmetry and exceptional points have so far been studied in systems larger than wavelength, such as coupled or modulated waveguides, WGM resonators and layered structures. These resonators are characterized by low energy leakage to surrounding space. Microparticles, in contrast, have very large radiative decay that has to be compensated by gain in the media to make the eigenfrequencies real. Here, the system parameters allowing to realize exceptional points and PT symmetry are studied theoretically in various composite microparticles, such as dimers of nanocylinders with gain and loss, using both analytical methods and full-wave simulations.

Laser-driven acceleration of electrons has been strongly pursued in the last few decades as a possible avenue to access to GV/m-scale accelerating gradients, reducing the size and the cost of the next generation of particle accelerators. Different coupling mechanisms to obtain synchronous interaction of longitudinal accelerating field with a traveling electron beam starting from an inherently transverse electromagnetic mode of the laser have been proposed, and have been successfully demonstrated experimentally. Metasurface-Laser-Acceleration (MLA) holds the promise for large gradients in excess of 1GV/m, with modest requirements in terms of laser energy and high wall-plug efficiency. Particularly, the MLA concept allows for obtaining acceleration gradients exceeding the amplitude of the driving field. The key advantages of this approach are the high field enhancement factor and consequent relaxed requirements on laser systems, the large number of degrees of freedom for tuning field amplitude and phase in time and space, and the availability of reliable and high precision instrumentation for nanofabrication of plasmonic material. A plasmonic-based accelerator operating at MHz repetition rate exhibit variety of potential applications ranging from electron microscopy to electron therapy.

When driven by few-cycle optical fields, nanoscale plasmonic antennas emit free-electrons having attosecond-scale temporal and nanometer-scale spatial resolution. I will review our recent work demonstrating the sub-optical-cycle, sub-femtosecond free-electron emission dynamics from plasmonic nanoantennas. We demonstrate the extreme temporal resolution of the photoemission process by sampling weak optical fields with attosecond resolution.

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To simulate nanoparticle interaction with an electron beam, we developed a theoretical description in the discrete dipole approximation for the general case of an arbitrary host medium. This theory allows fast numerical simulations of the experiments for particles inside a substrate, since there is no need to discretize the host medium. We implemented it in the open-source software ADDA to simulate electron-energy-loss spectroscopy and cathodoluminescence by particles of arbitrary shape and internal structure surrounded by arbitrary homogeneous host medium.

Cathodoluminescence (CL) imaging presents a powerful method to study the optical properties of a large variety of materials. The “white” free electron beam excitation source can be employed to locally excite structures making it an ideal tool to study resonant and dispersion properties of materials. In this talk, we will show the different approaches that can be used in CL imaging to measure dispersion and directionality in nanostructures. In particular, we will describe a novel approach we have developed in which the CL emission properties are measured in energy-momentum space. This technique is combined with polarization filtering to enhance the specificity of the technique. We show examples acquired on various nanophotonic geometries, including diffractive systems, incoherently emitting multilayer systems, and nanoantennas.

Smith-Purcell radiation (SPR) is generated by having free electrons pass on gratings. Based on SPR, the free electron laser and broadband light sources could be realized. Here, having electron beam fly through a nano-slot in Al grating, the high-order SPR has been extended to deep ultraviolet and the wavelength covers λ0≈230-1100nm with total output power of tens of nW. And we also investigate the SPR carrying orbital angular momentum (OAM) by applying the holographic gratings and the high-order coherent SPR in THz region by bunching the free electrons.

I shall discuss photothermal microscopy and its applications in detection, quantum yield measurements, plasmonic sensing and chirality studies.

For long, it has been sufficient to describe the physics of light absorption by metal nanoparticles using Maxwell equations, especially under cw illumination. Recently, new fields of research in thermoplasmonics were introduced leading the community to also focus on solid-state physics considerations to better describe electronic excitations, even under cw illumination. This presentation introduces the physics of light absorption by metal nanoparticles and how it has been complemented with the recent developments of applications such as hot-carrier assisted plasmonic chemistry and anti-Stokes thermometry.

Metasurfaces have enabled a remarkable new class of planar optics. Adding tunable or reconfigurable functionality is critical for many metasturface device applications. In this talk we describe three classes of thermal thermally tunable metastructures: 1) thermal free-carrier tuning of InSb-based ENZ/high-index heterostructures, 2) thermo-optic tuning of PbTe Mie resonators, and 3) metal-insulator transition enabled tuning of Ge/VO2 resonators. In all three cases we demonstrate large-magnitude thermal index tunability (dn/dT) relative to conventional thermo-optic effects in polymers or semiconductors. We conclude by demonstrating how both spatially uniform and non-uniform heating can be exploited in reconfigurable metasurface devices.

Single-particle optical spectroscopy methods are now enabling quantitative investigations of the optical, electronic, and vibrational responses of metal nano-objects. They were used here to investigate the internal thermalization and cooling dynamics of individual gold nanodisks supported on a sapphire substrate following their excitation by a femtosecond light pulse, and the transient optical response that they induce. The amplitudes and temporal profiles of the measured time-resolved signals were seen to present a large dependence on probe wavelength (particularly marked in the spectral range of the nanodisk localized surface plasmon resonance), which could be fully rationalized by numerical models describing both the ultrafast energy exchanges occuring within the nanodisk and with its supporting substrate and the induced transient changes of the nanodisk optical response. In particular, the measured time-resolved signals were shown to reflect a combination of the electron and lattice temperature evolutions (in the time range where they are both well-defined), with wavelength-dependent weights well reproduced by our models. The cooling kinetics of the nanodisks was seen to mainly depend on their thickness, in agreement with numerical simulations based on Fourier law of heat diffusion, also accounting for the presence of an interfacial thermal resistance between the nanodisks and their substrate. For the explored diameter range, the nanodisk cooling rate is limited by heat transfer at the gold–sapphire interface, whose thermal conductance could be estimated for each investigated nanodisk, showing small variations from one nanodisk to another.

Nowadays, the localized and efficient heat generation using optically-excited localized surface plasmon resonances (LSPR) is an active research field. Optically-excited plasmonic nanoparticles often show large resistive losses and consequently they can transform the optical energy into heat [1]. Strength and localization of heat generation strongly depend on the geometry and nanoparticle composition; therefore, different nanostructures can be designed to act as nanoheaters for specific purposes opening a wide range of fascinating applications. Some examples are micropollutants degradation [2] or plasmonic photothermal therapy [3]. The use of nanostructures as local thermal transducers often requires them to present a significant spectral tunability to work at the desire wavelength domain. In this talk, I will present our most recent results in this active topic, showing a thorough comparison of different efficient and tunable heating prototypes. [1] G. Baffou. Thermoplasmonics: Heating Metal Nanoparticles Using Light. Cambridge: Cambridge University Press, 2017. [2] H. Wei, Stephanie K. Loeb, Naomi J. Halas, J. Kim. Plasmon-enabled degradation of organic micropollutants in water by visible-light illumination of Janus gold nanorods. PNAS 117 (27) 15473, 2020. [3] André M. Gobin, Min Ho Lee, Naomi J. Halas, William D. James, Rebekah A. Drezek, and Jennifer L. West. Near-Infrared Resonant Nanoshells for Combined Optical Imaging and Photothermal Cancer Therapy. Nano Letters 7 (7), 1929, 2007.

In this talk I will review our recent studies of the physical models of basic time-modulated bulk circuit elements -- capacitors, inductors, and resistors -- and discuss potential applications of time-varying circuits for enhancing wireless transfer of power and information-carrying signals. In particular, we show that by periodically modulating the mutual inductance between the transmitter and receiver, the fundamental limits of classical wireless power transfer systems can be overcome. Regarding the second application, we consider a time-varying source for electrically small dipole antennas and show how time modulation can enhance the antenna performance.

Metasurfaces, the two dimensional versions of metamaterials, hold the promise of revolutionizing wave control by replacing conventional bulky components. However, they have found limited use in broadband applications due to their resonant, narrowband nature. An approach that can increase the aggregate bandwidth is to combine multiple resonant meta-atoms in the unit cell. By properly designing the resonances, the respective phase delays stemming from each resonance can combine into an increased, spectrally-constant group delay that can be exploited for achromatic delay and wavefront manipulation applications. Here, we demonstrate a concrete microwave realization of an achromatic time delay metasurface in reflection, by using five resonant meta-atoms to provide five spectrally-interleaved sharp resonances (three electric and two magnetic). The proposed metasurface exploits solely resonant phase delay, instead of propagating phase accumulation, leading to an ultrathin realization. We show delay of broadband, 700-MHz Gaussian pulses in the 10-GHz regime by 2 ns (20 times the carrier cycle), highlighting the practical potential of metasurfaces for dispersion control applications that rely on large and broadband phase delays.

Metasurfaces have been widely used to design low-profile antennas, thin absorbers, lenses etc. The operational frequency band of a metasurface is rather narrow due to its resonant nature. Loading metasurface unit cells with non-Foster elements allows for remarkable bandwidth extension. In this paper, design of a broadband metasurface to operate as an artificial magnetic conductor is considered. The main issues which influence the bandwidth extension such as implementation of the non-Foster load, minimization of conversion error of a negative impedance converter, and circuit stabilization are addressed.

Negative index metamaterials boosted novel theoretical and experimental investigations across different disciplines. One peculiar application, which seemed to be especially attractive, is radar invisibility. Over the years, however, it become clear that real radar systems are not deceived with negative index metamaterials and, probably, this approach is not a way to go. Here we will present our endeavours on real-life radar systems deception. Our strategy is based on time-varying metasurfaces, which allow us concealing a macroscopic 1m^2 target from an integrating system. Both theoretical and experimental results will be shown. Other concepts will be discussed and revised.

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In the last years, spatially modulated metasurfaces have shown a great potential for electromagnetic field manipulation through low losses thin structures. In particular, the interaction with a periodically modulated metasurface can induce a controlled spectral shift in an electromagnetic field, giving rise to interesting phenomena like anomalous reflection/refraction and conversion from surface wave to leaky wave, with important applications in the antenna and propagation fields. All these phenomena can be described in a unified manner through the Floquet Wave (FW) expansion of the fields and currents. The objective of the metasurface design can then be formulated in terms of the desired FW coefficients. This talk will illustrate an effective way to perform the periodic metasurface design, based on the description of the metasurface through homogenized impedance-type boundary conditions. Applicative examples will be also presented.

Topological photonic state (TPS) is a new type of confined state with one-way transport characteristics, being immune to backscattering from disorders, obstacles, and defects. Here we introduced our recent works on exploring magneto-optical (MO) microstructure as an important platform for realizing TPSs and exploring their novel physical properties. We have constructed and revealed the microscopic physical images of chiral TPS in infinite, semi-infinite, single-cylinder and photonic crystals from the point of view of energy flux. We have analytically solved the EM wave scattering equation of a single MO cylinder. We discovered a windmill-like EM wave scattering phenomenon with topological characteristics and revealed its mathematical and physical origins. These results can help us quantitatively understand the TPSs in MO microstructures based on electrodynamics, electromagnetism and optics. We further discuss the formation of antichiral TPS by applying opposite magnetic fields to two triangular sublattices A and B in a honeycomb MO photonic crystals and breaking the sublattice symmetry, and unique slow-light TPS constructed from strong interaction of two TPSs. Our works provide a new perspective for understanding TPSs in MO microstructures and broaden the current understanding of TPSs, and are expected to provide useful guidance for designing the topological photonic devices with excellent performance.

In this talk I will consider space-time metamaterials of travelling-wave type and introduce the theory of homogenisation of these modulated media [1]. This framework provides analytical expressions for the effective permittivity, permeability and magnetoelectric coupling of these media in the long wavelength limit. From the derived parameters we will see how it is possible to achieve nonreciprocal effects away from the asymmetric band gaps, and even down to the quasistatic limit if both the permittivity and permeability are modulated, and how the synthetic motion present in these systems allow us to make a link to the Fresnel drag effect of light in moving media [2]. Our theory unveils a regime where the modulation speed approaches that of waves in the background medium where homogenisation breaks down and a new mechanism for gain emerges [3], enabling a form of nonreciprocal broadband amplification that could be realised in graphene [4]. On the other hand, temporal only modulations enable novel ways to excite surface waves from the far field [5]. [1] Huidobro et al, arXiv:2009.10479 (2020). [2] Huidobro et al, Proceedings of the National Academy of Sciences 116 (50) 24943-24948 (2019). [3] Pendry et al, arXiv:2009.12077 (2020). [4] Galiffi et al, Physical Review Letters, 123, 206101 (2019). [5] Galiffi et al, Physical Review letters 125, 127403 (2020).

Since the seminal work by Ashkin on optical force and trapping, this field has witnessed and supplied evolutionary contributions to versatile micromanipulation and biomedical applications. Even so, little information is available and only with regards to trapping the nanoparticles, not in discriminating their chiralities. Recently, it shows that chiral particles in microscale can be optomechanically separated under circularly polarized light. However, downsizing this mechanism to nanometer-sized objects appropriate for chiral specimens in nature confronts a few formidable challenges. For instance, the non-chiral gradient force dominates over chiral force since chiral polarisability is much weaker than electric polarisability. Herein, we feel fortunate to enter this interesting field, which is proved in our work to be promising in taking one step forward for separating the sub-2 nm enantiomers using a metasurface composed by an array of silicon (Si) nanodisk embedding with off-centered holes, which supports sharp high-quality resonance. This echoes with emerging demands from practical applications to exploit new and practical mechanisms of sorting of chiral nanoparticles.

Interfaces between ferromagnetic metals and nonmagnetic specimen attract much attention as they are very important for the formation of magnetic properties of nanostructures. Vice versa, specific magnetic ordering at such interfaces may provide new effects in their optical and nonlinear optical response. In this work we study the magnetization-induced effects in optical second harmonic generation (SHG) in W/Co/Pt-based thin films with the thicknesses of the Co layer of $2-10 \; nm$. Besides common \textit{odd} in magnetization effects in the SHG intensity, we observe additional one that is not expected for homogeneously magnetized ferromagnetic films, which consists in modulation of $p$-polarized SHG intensity under longitudinal magnetic field application. The phenomenological description of the observed effect is performed in terms of gradient and second-order in magnetization contributions to the SHG polarization, where gradient of magnetization along the normal to the structure plays the key role.

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Metasurfaces exhibiting strong nonlinear effects are a rapidly developing part of nonlinear optics. The design freedom they provide allows tuning of a wide range of nonlinear processes, such as harmonics generation, and nonlinear wavefront control. High-Q metasurfaces are often used to enhance nonlinear processes, however such structures are fundamentally limited by their low bandwidth and therefore cannot effectively couple to short pulses. Here we propose a high-Q all-dielectric metasurface with a Q-factor that can be rapidly increased while retaining the energy trapped in it’s resonant mode, thereby combining the broadband aspect of low-Q metasurfaces with the field enhancement of high-Q metasurfaces. Using coupled mode theory (CMT), we show the capacity of a resonance with a dynamically changing Q-factor to achieve an increase in second harmonic generation efficiency. We then propose an all-dielectric metasurface consisting of silicon and germanium that exibits a resonance, the quality factor of which can be increased by injecting free carriers in germanium. We study this structure using FDTD with dynamically changing permittivity and show that an increase in total generated second harmonic by a factor of 1.5 as compared to the unperturbed resonance can be achieved.

We provide an overview of photonics research based on free electrons, supplemented by original theoretical insights and discussion of several stimulating challenges and opportunities. In particular, we show that the excitation probability by a single electron is independent of its wave function, apart from a classical average over the transverse beam density profile, whereas the probability for two or more modulated electrons depends on their relative spatial arrangement, thus reflecting the quantum nature of their interactions. We derive first- principles analytical expressions that embody these results and have general validity for arbitrarily shaped electrons and any type of electron−sample interaction. We conclude with some perspectives on various exciting directions that include disruptive approaches to noninvasive spectroscopy and microscopy, the possibility of sampling the nonlinear optical response at the nanoscale, the manipulation of the density matrices associated with free electrons and optical sample modes, and appealing applications in optical modulation of electron beams, all of which could potentially revolutionize the use of free electrons in photonics.

This talk is divided into two parts: one exploring how quantum shaping of free electrons leads to enhanced light production, and another exploring how free electrons can lead to shaping of quantum light. In the first part, we show how suitably engineered wavefunctions of free-electrons can strongly control the directionality and monochromaticity of the radiation they emit when they are accelerated. This occurs as a result of intentionally designing the structure of the wavefunction to allow for quantum interferences between transition amplitudes leading to radiation of the same photon. Such phenomena could lead to novel quantum-enhanced Bremsstrahlung sources, synchrotrons, and free-electron lasers. In the second part of the talk, we discuss how the unique ladder energy-like level structure of quantum free electrons allows for a unique form of “velocity blockade” during quantum multiphoton emission, allowing for production of light with very low noise beyond the classical limit. This provides a novel route towards generating and shaping non-classical states of light. These two parts together provide a powerful outlook on new possibilities in the field of light sources based on the truly quantum interactions of electrons and light.

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We discuss new means to accelerate vortex electrons with orbital angular momentum (OAM) to ultrarelativistic energies and to produce vortex ions, protons, and other charged particles heavier than electron. This can be done by adapting the techniques used to manipulate classical beams in accelerators and electron microscopes. In particular, we show that both the OAM and a mean emittance of the wave packet are conserved in axially symmetric fields of electric and magnetic lenses, as well as in Penning traps. We analyze quantum dynamics of the packet's rms radius $\langle\rho^2\rangle$, relate this dynamics to a generalized form of the van Cittert-Zernike theorem, applicable at arbitrary distances from a source and for non-Gaussian packets, and adapt the Courant-Snyder formalism to describe the evolution of the packet's phase space. The vortex beams can therefore be accelerated, focused, steered, trapped, and even stored in traps somewhat analogously to the classical angular-momentum-dominated beams. We also give a quantum version of the Busch theorem, which states how one can produce vortex ions and protons by using a magnetized stripping foil employed to change a charge state of ions.

The modulation and engineering of the free-electron wave function bring new ingredient to the electron-matter interaction. We consider the dynamics of a free-electron passing by a two-level system fully quantum mechanically and study the enhancement of interaction from the modulation of the free-electron wave function. In the presence of resonant modulation of the free-electron wave function, we show that the electron energy loss/gain spectrum is greatly enhanced for a coherent initial state of the two-level system. Thus, a modulated electron can function as a probe of the atomic coherence. We further find that distantly separated two-level atoms can be entangled through interacting with the same free electron. Effects of modulation-induced enhancement can also be observed using a dilute beam of modulated electrons.

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We demonstrate optically tunable control of second-harmonic generation in all-dielectric nanoantennas: by using a control beam which is absorbed by the nanoresonator, we thermo-optically change the refractive index of the radiating element to modulate the amplitude and the phase of the second-harmonic signal. For a moderate temperature increase, sizeable modulation is demonstrated; this large tunability of the single meta-atom response paves the way to exciting avenues for reconfigurable homogeneous and heterogeneous metasurfaces.

In many workplaces lasers are increasingly becoming an existential threat, potentially causing injuries or damaging instruments. In order to protect people and instrumentation from high, potentially hazardous, intense light, self-activating devices – relying on the automatic activation upon intense light illumination – are of paramount importance. We propose an optical device composed of a multilayer structure featuring VO2, a material experiencing a metal to insulator phase transition around ~70° C. The working principle relies on the structure heating due to external radiation. When the latter intensity exceeds a threshold value, the temperature in the structure overcomes the VO2 critical temperature. Thus the switch from the insulating phase to the metallic one occurs, yielding an important increase of reflectivity accompanied by a significant reduction of transmitted light. We optimize the structure’s geometrical parameters to optimize the device performance.

We develop a model describing non-equilibrium processes under the excitation of resonantsemiconductor nanostructures with ultrashort laser pulses. We focus on the heating effects related topulsed excitation with account on free carriers generation, thermalization, and relaxation. The heatexchange between the electron and phonon system is treated within the two-temperature model. Weapplied the developed model to describing pulsed heating of silicon nanocylinder on top of a dielectricsubstrate. We come up with estimations of the thermal damage threshold of the considered structureswhich provides the limits for the experimental conditions and ensures thermal stability of the samples.

Nonlinear light-matter interactions are essential toward communication, sensing, imaging, etc. The conventional method of quantifying optical nonlinearity is z-scan, which typically works with thin films, and thus acquires ensemble nonlinear responses, not from single nanostructure. Here we present an x-scan technique that is based on a confocal laser scanning microscope with both forward and backward detections, offering simultaneous quantification for nonlinear behavior of scattering, absorption and total attenuation from a single nanostructure. From x-scan, we found exceptionally strong nonlinear scattering/absorption in plasmonic and silicon nanostructures via photothermal and thermo-optical interactions. Potential applications, including high-contrast all-optical switching and non-bleaching super-resolution microscopy, are demonstrated.

Recent advancements in nanofabrications, characterisations and computer modellings allow generating of novel metasurfaces that control the light characteristics in extraordinary ways. Such advances have led to revolutionary applications in several fields, including but not limited to metalenses, polarisation converters, nano-sensors, and holograms. Meanwhile, the active and reversible tunning of metasurfaces has attracted significant attention due to the larger degree of freedom, which tunable metasurfaces can offer. Tunning metasurfaces can be obtained by various external stimuli, such as mechanical, electrical, optical, etc. This talk will review our recent achievements on employing temperature for controlling the light-matter interactions in dielectric and hybrid metallo-dielectric metasurfaces. First, I demonstrate how the encoded transmission pattern can be tuned by controlling a dielectric metasurface's temperature. Through exploitation of the thermo-optical properties of silicon, we have achieved complete control of the images' contrast by altering the metasurface temperature. Subsequently, I demonstrate how hybridisation of plasmonic nanostructures with semiconductor and dielectric nanoparticles and using the temperature as a versatile tool enables performing biochemical detecting with extremely high sensitivity. I will show that integrating ultra-porous dielectric nanoparticle networks can significantly increase the optical response enabling detections of plasmonic resonances down to the 10^-8 refractive index variations at certain temperatures. In summary, I demonstrate that temperature tuning can play a significant role in novel applications of metasurfaces ranging from flat optical devices e.g. metalenses and metaholograms, to ultrasensitive optical sensors.

On two new optical forces acting on magnetoelectric particles Manuel Nieto-Vesperinas1, Xiaohao Xu2, Cheng-Wei Qiu3 1.Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas (CSIC), Madrid 28049, Spain. 2.Institute of Nanophotonics, Jinan University, Guangzhou 511443, China. 3.Department of Electrical and Computer Engineering, National University of Singapore Singapore 117583, Singapore. We show two new optical forces that we have recently discovered. One derives from a vortex density of azimuthal imaginary Poynting momentum (IPM) which we show to be built by a superposition of radially and azimuthally polarized beams. Further this azimuthal IPM density may exist with a donut beam intensity distribution, and with zero azimuthal component of all other momenta. This discovery is important because while the spin momentum of a light beam loops in circularly polarized beams and the orbital momentum spirals in helically phased beams, such a behavior of the IPM had not yet been found. The resulting novel effect for optical manipulation is the rotation of spherical particles in absence of incident spin and orbital angular momenta. The second force that we address derives from the interference between the electric and magnetic dipoles induced by light in a magnetodielectric particle, (which gives rise to those well-known Kerker interference effects in the angular distribution of scattered intensity), producing an intensity gradient force which, in contrast with the well-known gradient force employed in standard optical tweezers, is either attractive or repulsive, as well as non-conservative on illumination of the object with either linearly or elliptically polarized Gaussian beam. This new force is directionally anisotropic, tending to repel particles away from the beam axis. Such repulsive effects enhance the sensitivity of the optical manipulation configuration to the particle size. On the basis of this behavior, all-optical sorting of Si nanoparticles is theoretically demonstrated, with tunable size-selection criterion and accuracy.

Thermally activated transitions are ubiquitous in nature, driving several conformational or functional changes important for life. From a physical perspective, understanding the role of fluctuations in the dynamics of nonlinear systems with multiwell energy landscapes is of paramount importance in many disciplines of both fundamental and applied sciences. For instance, it has been recognized that thermal noise is responsible for the activation of transitions in a wide variety of processes at mesoscopic scale, such as the magnetization reversals in thin films, molecular reactions, protein folding, colloid adsorption at fluid-fluid interfaces, drug binding, photochemical isomerization, to name but a few. Often thought as the escaping process of a Brownian particle from a well, thermally activated transitions typically occur in complex environments which for simplicity are nonetheless conceived as ideal Newtonian, memoryless, fluids. When the process takes place in Newtonian fluids the escaping process is well described by Kramers theory, but this is not the case when memory is involved. Using optical trapping and a framework based on the Generalized Langevin Equation, in this contribution we show that a worm micellar fluid exhibiting memory friction may give rise to transitions that are much faster than those expected in Kramers theory. We show that a non-homogeneous frequency-dependent mobility that drastically increases around the energy barrier is the responsible for these fast transitions. These findings provide a major understanding of barrier crossing processes under more realistic conditions that should expand our comprehension of plenty of transport mechanisms in nature [Brandon et al. Phys. Rev. Lett. 126, 108001].

We consider the simulation of scattering of the high-order vector Bessel beams in the framework of the discrete dipole approximation (DDA). For this purpose, a new general classification of all existing types of Bessel beams was developed based on the superposition of transverse Hertz vector potentials. Next, we implemented these beams in the ADDA code – an open-source parallel implementation of the DDA. This enables easy and efficient simulation of Bessel beams scattering by arbitrary-shaped particles. Moreover, these results pave the way for the following research related to the Bessel beam scattering near a substrate and optical forces.

Photonic force microscopy accurately measures forces down to the femtonewton range, allowing several advances in biophysics, soft-matter and nanotechnology. The precision of this kind of force measurement is crucially dependent on the quality of the signal arriving at the detector. The backscattering configuration, even if more difficult to implement, is necessary when optical forces must be measured close to membranes or to an opaque or reflective surface. In this last case, a source of signal noise could be the interference, on the detector, of light backscattered by the trapped particle and light reflected by the surface. This effect could be eliminated by spatially filtering the signal, but this procedure has the obvious drawback of reducing the signal intensity, worsening the signal to noise ratio. Here, we use Gaussian and Cylindrical Vector Beams (CVBs) to trap a standard latex bead close to a weakly reflective surface. We show that signal oscillations, due to the interference between light backscattered by the bead and light backreflected by the surface, are reduced when CVBs are used. Moreover, trap spring constants and particle fluctuations are measured. Experimental results are compared with the modelling of electromagnetic backward scattering in the T-matrix formalism. These results may open the way to the application of photonic force microscopy to more complex surfaces, such as those encountered in the study of metamaterials. We acknowledge funding from the agreement ASI-INAF n.2018-16-HH.0, project “SPACE Tweezers”.

Nowadays, there are different techniques of contactless manipulation of objects over a wide range of sizes. In particular, optical and acoustical traps cover complementary size ranges with a small overlapping. Namely, while optical techniques are useful for trapping from single atoms and molecules up to particles of the order of tens of microns, acoustic techniques have been used for trapping particles from tens of microns up to few millimeters, the former in liquid with ultrasonic frequencies of MHz and the latter in air with frequencies of kHz. But what are the practical limits of the largest objects that can be acoustically trapped? By exploiting some analogies with the more developed optical traps, we used the Generalized Lorentz-Mie Theory (GLMT) for calculating the acoustic forces in the ultrasonic standing-wave levitation trap and performed a thorough experimental study with the aim of giving an answer to that question. We demonstrate that the acoustic force exhibits sign-inversions as a function of particle size, which means that particles can be trapped either in pressure nodes or antinodes. This is analogous to the particle size-effect found in periodic optical traps, but in the case of acoustics, it also unveils the relevant role of mechanical resonances. Our theoretical and experimental results show excellent agreement.

A general method to realize arbitrary dual-band independent phase control is proposed and demonstrated. There are two steps to accomplish the proposed independent phase control at two frequencies. The first step consists in introducing a frequency-independent phase control mechanism and the second step consists in controlling the phase difference at two selected frequencies varying in full phase range. A double-layered C-shape reflective geometric phase meta-atom is designed to realize independent phase control at 6.6 GHz and 8.4 GHz in the full phase range, whose working efficiencies are high in both two bands. The frequency-independent phase control mechanism is accomplished through geometric phase principle and the phase difference control is realized through different linear cross-polarization response at the two frequencies. As a proof-of-concept, we propose two functional metasurfaces in the microwave region. The first metasurface (MTS1) performs beam steering with different directions at two frequencies. The second metasurface (MTS2) generates achromatic beam steering at two frequencies. The performance of two metasurfaces are studied from 6.1 GHz to 7.1 GHz (Band Ⅰ) and from 7.9 GHz to 8.9 GHz (Band Ⅱ). Both simulation and measurement results agree well with the theoretical pre-settings and the maximum measurement efficiencies of MTS1 and MTS2 are 88.7%, 91.0% in Band Ⅰ and 92.3%, 89.8% in Band Ⅱ, respectively. The dual-band metasurface designs suggest favorable practical dual-band applications for their high efficiency and low profile (4 mm thickness) features. As such, the proposed scheme for dual-band independent phase control provides a new way to practical applications of modern wireless communication systems.

A phase compensation method for 1-bit phase quantized transmitarray is discussed. Using the tiled architecture of the transmitarray, the position of each unit cell is changed along the optical axis of the transmitarray. The spatial displacement allows changing the resulting phase distribution along the transmitarray aperture. Analytical calculations were performed to demonstrate the performance of the transmitarray radiation pattern.

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Modulated reactance synthesis for planar impenetrable electromagnetic surfaces for endre radiation characteristics is presented. It is based on aperture field synthesis over the entire spectral range, where the desired radiation pattern is prescribed by a traveling-wave current over the aperture. Carefully constructed auxiliary waves in the evanescent spectrum are added and the total aperture fields are optimized such that the entire aperture surface becomes pointwise reactive. The optimized aperture fields define the modulated surface reactance that realizes the desired pattern when excited by a feed surface wave. The reactance distribution may be realized as modulated metasurfaces.

A method for the estimation of sheet impedance of thin sample which does not require a direct contact with the sample under test is proposed. The surface impedance is calculated through an inversion procedure that exploits the scattering parameters obtained through a waveguide measurement setup. An inversion procedure based on the representation of the waveguide-air-waveguide section as a π junction is employed. In order to prevent the field leakage from the ai gap created for histing the thin sheet, an EBG surface is introduced on the flange of the waveguide. The EBG parameters are selected in order to guarantee a stop-band in the frequency range of interest. It is shown how the introduction of the EBG surface allows to improve the estimation of the surface impedance of the thin sheet with respect to the case without EBG.

It is well known that, by using the Babinet’s principle, the addition of the transmission coefficients of two complementary metallic metasurfaces is equal to 1. This fact can be rigorously demonstrated for the case of infinitesimally thin screens made of perfect electric conductor. If we were interested in all-dielectric metasurfaces then it is not rigorous. Nevertheless, in this talk, we will present an approximated theory which demonstrates the validity of the Babinet’s principle when the two complementary screens are made of two different high-permittivity materials and the word “complementary” means just the interchange of those two materials. We will also provide a numerical validation of this theory.

Following our recent discovery of the Hyper Rayleigh Scattering Optical Activity (HRS OA) [1], further developments[2] and related, new nonlinear chiroptical effects will be reported. HRS OA states: “Upon illumination with circularly polarized light, the intensity of light scattered at higher harmonics depends on the chirality of the scatterers”. HRS OA is the most fundamental nonlinear chiroptical effect because all other nonlinear chiroptical effects are more restrictive and therefore less fundamental. For instance, HRS OA is a scattering effect, hence there is no need for coherence in the frequency conversion process; contrary to any of the second, third, fourth, etc. harmonic generation effects. Additionally, HRS OA is a parametric process. Since the excitation takes place via virtual states, there is no restriction on the frequency of incident light. By contrast, other nonlinear scattering effects, such as two-photon circular dichroism and hyper-Raman are non-parametric - they require real energy states that restrict the frequencies at which these effects occur. [1] J. T. Collins, K.R. Rusimova, D.C. Hooper, H.-H. Jeong, L. Ohnoutek, F. Pradaux-Caggiano, T. Verbiest, D. R. Carbery, P. Fischer, V. K. Valev, “First Observation of Optical Activity in Hyper-Rayleigh Scattering”. Phys Rev. X 9, 011024 (2019) [2] L. Ohnoutek, N. H. Cho, A. W. A. Murphy, H. Kim, D. M. Răsădean, G. D. Pantoş, K. T. Nam, V. K. Valev, “Single Nanoparticle Chiroptics in a Liquid: Optical Activity in Hyper-Rayleigh Scattering from Au Helicoids”. Nano Lett. 20, 5792–5798(2020)

Spin and orbital angular momentum (SAM and OAM) are intrinsic properties of light which provide new degrees of freedom for enhancing the information capacity in optical communications, and for empowering optical manipulations of micro and nanoscale particles. In linear optics, the angular momentum of light can be easily manipulated through the optical spin-orbit interaction (SOI) in structured media such as liquid crystals, metasurfaces and forked gratings. Similarly, metasurfaces can be used to generate nonlinear optical beams with both custom-defined SAM and OAM states. However it has been limited to a low-order process in which only a Gaussian-shape fundamental wave is used. Here, we study the high-order nonlinear optical SOI on metasurfaces and demonstrate the generation of multiple angular momentum states in nonlinear waves. This is achieved by exploiting the freedom provided by both the SAM and OAM states of FW and the topological charges of the plasmonic metasurfaces. The mechanism of both intrinsic and extrinsic contributions to the OAM of the nonlinear waves is revealed. High-order nonlinear SOI on metasurfaces offers new opportunities for realizing ultra-compact nonlinear vortex beams.

Motivated by the theoretical observation that isotropic chirality can exist even in completely random systems, a dielectric metamaterial consisting of a random colloid of meta-atoms is designed, which exhibits unprecedentedly high isotropic optical activity. Each meta-atom is composed of a helically arranged cluster of silicon nanospheres. Such clusters can be fabricated by large-scale DNA self-assembly techniques. It is demonstrated that the use of a high concentration of the meta-atoms in the colloid provides significant suppressions of incoherent scattering losses. As a result, the proposed system shows three orders of magnitude improvement of isotropic optical activity as compared with the previous metamaterial designs. This work highlights the significant potential of completely random systems, which are commonly produced in colloidal sciences, for applications as metamaterials toward novel photonic effects and devices.

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Please see the attched file.

Dielectric metasurfaces offer a promising alternative platform for optical biosensing to plasmonic counterparts with several advantages including: reduced optical losses, CMOS compatibility and reduced heating At the same time, the sensing mechanism is substantially different to plasmonic antennas for which the sensitivity stems predominantly from the properties of isolated particles, All-dielectric nanoantennas bulk sensitivity is negligible. Hence, they require an additional scattering channel e.g. multiple scattering within nanoantenna arrays or coupling to a substrate to exhibit sufficient sensitivity for practical applications. In this work, we scutinize this mechanizm and theoretically study the factors that influence the sensitivity of substrate-supported dielectric metasurfaces. We also investigate a different scheme of biosensing utilizing circular dichroism enhanced by a dielectric metasurface. It has been recently theoretically shown that an efficient chiral sensing scheme may be based on overlapping the magnetic and electric response of a nanoantenna in a manner similar to the Kerker effect. At the same time, experimental investigations show that the presence of a substrate mitigates this capability and yet significant chiral sensing enhancement can be observed, indicating that a different mechanism must be involved. Here, we focus on the role of the substrate mediated coupling to find out how the presence of the substrate affects the circular dichroism based sensing with dielectric metasurfaces. We propose a modified version of our efficient T-matrix based approach to study such chiroptical effects in dielectric metasurfaces.

Recently, the physical significance of dynamic toroidal multipoles in the context of electrodynamics has been put under discussion. Indeed, the latter can be shown to arise simply from a Taylor series of the exact source (Cartesian) multipole moments. The split into elementary and toroidal parts was demonstrated to lead to an unphysical result were forbidden components of the momentum transform of the current could radiate into free space. In this contribution, we elaborate the conditions that a current distribution must necessarily satisfy to be considered a ‘pure’ toroidal dipole source. We demonstrate for the first time that symmetry prevents such current distribution to radiate as an elementary electric dipole moment, without leading to an unphysical result. Thus, while both elementary electric dipole and toroidal dipoles are indistinguishable outside the source, they display topologically distinct characteristics within the smallest spherical surface enclosing the source itself and have different physical origin. Based on our results, a pure ‘toroidal’ source can be designed. We believe the outcome of our investigations will help clarify further the formal meaning of the toroidal multipoles.

Systems consisting of spinning units provide a promising direction to create novel active materials with exotic materials properties. In this talk, I will present our recent results concerning the hydrodynamics of torque driven spherical spinners. Using computer simulations, we demonstrate that hydrodynamic interactions, at weakly inertial regime, give a rise to directional particle-particle interactions. These lead to a rich phase behaviour. In 3-dimension, a spontaneous formation of particle vortices is observed at low volume fractions, while a phase separation to coexisting high and low density crystals is observed in a carpet of sedimented particles near a surface. Finally, and time allowing, I will discuss a strongly confined system, where the particles form spinning pairs when confined between two walls along the spinning direction. These pairs can synchronise their rotation. In the case of non-perfect global synchronisation, the formation of topological defects, akin to polar active nematics, is observed. These, in turn, can lead to large scale particle flows.

Chiral edge states can transmit energy along imperfect interfaces in a topologically robust and unidirectional manner when protected by bulk-boundary correspondence. However, in continuum systems, the number of states at an interface can depend on boundary conditions. Here we design interfaces that host a net flux of the number of modes into a region, trapping incoming energy. As a realization, we present a model system of two topological fluids composed of counter-spinning particles, which are separated by a boundary that transitions from a fluid-fluid interface into a no-slip wall. In these fluids, chiral edge states disappear, which implies non-Hermiticity and leads to a novel interplay between topology and energy dissipation. Solving the fluid equations of motion, we find explicit expressions for the disappearing modes. We then conclude that energy dissipation is sped up by mode trapping. Instead of making efficient waveguides, our work shows how topology can be exploited for applications towards acoustic absorption, shielding, and soundproofing.

We use prestress to induce spontaneous deformations in mechanical metamaterials made of bistable building blocks. The choice of building block geometry and the spatial arrangement of blocks sets the frustration in the corresponding spin system. Geometries that map to spin systems with ordered ground states result in competing local orientations, which are separated by domain walls. By tuning the stiffness of elements in the unit cell, we change the domain wall morphology from a binary, strictly spin-like regime, to a more continuous, elastic regime. In the elastic regime, we inject, manipulate, and expel domain walls via textured forcing at the boundaries. The system exhibits dynamical hysteresis, and we demonstrate a forcing protocol that produces multiple, topologically-distinct steady cycles, which are protected by the differences in their internal domain wall arrangements. These distinct steady cycles rapidly proliferate as the complexity of the applied forcing texture is increased, thus suggesting that such mechanical systems could serve as useful model systems to study multistability, glassiness, and memory in materials.

Active solids consume energy to allow for actuation, shape change, and wave propagation not possible in equilibrium. For two-dimensional active surfaces, powerful design principles exist that realise this phenomenology across systems and length scales. However, control of three-dimensional bulk solids remains a challenge. Here, we develop both a continuum theory and microscopic simulations that describe an active surface wrapped around a passive soft solid. The competition between active surface stresses and bulk elasticity leads to a broad range of previously unexplored phenomena, which we dub active elastocapillarity. In passive materials, positive surface tension rounds out corners and drives every shape towards a sphere. By contrast, activity can send the surface tension negative, which results in a diversity of stable shapes selected by elasticity. We discover that in these reconfigurable objects, material nonlinearity controls reversible switching and snap-through transitions between anisotropic shapes, as confirmed by a particle-based numerical model. These transition lines meet at a critical point, which allows for a classification of shapes based on universality. Even for stable surfaces, a signature of activity arises in the negative group velocity of surface Rayleigh waves. These phenomena offer insights into living cellular membranes and underpin universal design principles across scales from robotic metamaterials down to shape-shifting nanoparticles.

Active matter systems are composed of particles, called agents, which consume energy from the surroundings and convert it into motion. Initially inspired by biological systems, the study of active matter has become one of the fastest growing fields in soft condensed matter physics. To date, with a variety of models describing the collective behavior of active matter, different types of biological and artificial agents have been studied and developed [1]. Active matter agents use different self-propulsion mechanisms [2]. The majority of biological micro-swimmers use either rotating or beating flagella to move through a liquid. On the other hand, synthetic active particles commonly use other physical phenomena, including inhomogeneous catalysis of chemical reactions, or diffusiophoresis, thermal inhomogeneity, or thermophoresis, and mechanical motion induced by external fields. We propose [3] a type of active matter agents that use magnetohydrodynamic (MHD) forces for propulsion. The agents are resonantly excited by an electromagnetic wave and produce crossed electric and magnetic fields in their own vicinity. The electric field generates currents in the surrounding fluid, which in turn interact with the magnetic field and produce the reaction force (see Fig. 1). We show that this force generally has a non-zero average over the period of oscillations and thus can provide steady motion of the agents. We have developed analytical models of the agent orientation in the external fields and the appearance of the MHD force. Finally, we have examined and verified the proposed concept through simulations.

An introduction will be given to the quantitative analysis of plasmons with electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope STEM). Experimental results will be presented along with theoretical calculations, with the aim of providing deeper insight into the dynamics of electrons in localized surface plasmons.

The decay of localized surface plasmons in metallic nanoparticles can result in the generation of energetic or “hot” electrons and holes. These carriers can be harvested and harnessed for applications in photovoltaics, photocatalysis and light sensing. To optimize hot carrier production in devices, a detailed theoretical understanding of the relevant microscopic processes, including light-matter interactions, plasmon decay and hot electron thermalization, is needed. In the first part of my talk, I will describe a material-specific theory of hot-carrier generation in metallic nanoparticles. This approach combines a classical description of the light field with a quantum-mechanical treatment of the electrons. Combining this approach with materials screening techniques has enabled the discovery of efficient photocatalysts based on bi-metallic core-shell nanoparticles. In the second part of my talk, I will describe our efforts to develop a fully quantum-mechanical description of plasmon decay which can be used to describe hot carrier generation in a nanoparticle with a single plasmon quantum.

Nanoparticles are highly relevant for applications in, e.g., catalysis, sensing, and energy harvesting due to their size, shape, composition, and environment sensitivity providing platform for material optimization and targeted design of functionalities. We study localized surface plasmon resonances (LSPRs) of nanoparticles, which can decay into high-energy electrons and holes allowing hot-carrier generation for, e.g., photocatalysis. Here, we will show work in which we follow plasmon formation as a collective Coulomb renormalized excitation, track its subsequent decay into weakly interacting electron-hole transitions, and finally, obtain the corresponding hot-carrier distributions [1], all within time-dependent density functional theory (TDDFT). Our work paves the way for addressing the spatiotemporal dynamics of hot-carrier generation in catalytically-relevant edge and corner sites, and allows to study hot-carrier injection via direct transfer between nanoparticles [2] or between a nanoparticle and a molecule [3]. A major difficulty in interpreting plasmonics in finite nanoscale systems is the vast number of excitations. Going beyond from our previous analysis [4], I will also discuss upcoming work, where we transform the canonical equations of motion into polaritonic form, with collective plasmonic, hot carrier, and charge transfer excitation coordinates to and from the frontier molecular orbitals of the reactants. Subsystems allow us to discuss thermodynamical properties such as work, heat, and efficiency. We are also in process of combining systems with longitudinal plasmonic fields [5] with transverse EM-fields, extending the the framework towards previously developed QEDFT [6]. To this end, I will briefly introduce our code development efforts aiming for unified framework with high throughput supporting multipolar response functions of molecules, transverse cavity modes, and molecular dynamics on cavity-polaritonic-electronic zero-point energy surfaces. [1] Hot-Carrier Generation in Plasmonic Nanoparticles: The Importance of Atomic Structure, Rossi, Erhart and Kuisma, ACS Nano 14, 9963 (2020) [2] Plasmon-Induced Direct Hot-Carrier Transfer at Metal-Acceptor Interfaces, Kumar et al., ACS Nano 13, 3188 (2019) [3] Direct hot-carrier transfer in plasmonic catalysis, Kumar et al., Faraday Discussions 214, 189 (2019) [4] Kohn–Sham Decomposition in Real-Time Time-Dependent Density-Functional Theory: An Efficient Tool for Analyzing Plasmonic Excitations, Rossi et al. J. Chem. Theory Comput. 13, 4779 (2017) [5] Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling, Fojt et al., Journal of Chemical Physics 154, 094109 (2021) [6] Quantum-electrodynamical density-functional theory: Ruggenthaler et al. Bridging quantum optics and electronic-structure theory Phys. Rev. A, 90, 012508 (2014)

Internal surface photoemission of electrons from metal into semiconductor through discrete states (Tamm surface states or discrete energy levels in Quantum Well) at the interface is considered. Resonant tunneling of electrons through the states can enhance substantially the efficiency of hot carrier generation for application in photocatalysis

Highly-absorbing, plasmonic-metal nanostructures offer a promising route to relax the challenging constraints imposed on semiconducting photocatalysts by both light-absorption and band-alignment conditions. In fact, it has been recently demonstrated that plasmon non-radiative decay generates highly energetic hot carriers that can be transferred to either an adjacent semiconductor (sensitization) or an adsorbed molecule, in the latter case altering the chemical reaction pathway. Hence plasmonic hot carriers turn metallic nanostructures into novel photocatalysts and can have a dramatic impact for solar fuel applications. To adequately harness these energetic, non-equilibrium carriers, fundamental knowledge of their energy distributions, dynamics and associated lifetimes is necessary. In this talk we will give an overview of hot electron and hot hole devices and explore their potential for photocatalysis. In particular, we will present recent results on the use of copper as a plasmonic catalyst [3,5] and discuss emerging directions in plasmonic catalysis.

See abstract attached.

In his seminal paper “More is different”, Anderson pointed out that “The behavior of large and complex aggregates of elementary particles, it turns out, is not to be understood in terms of simple extrapolation of the properties of a few particles.” Analogously, such statement also correctly describes optical binding with many particles. Proposed by Burns et al., the field of optical binding deals with how Lorentz force stably binds multiple microparticles into a single entity. We discovered that the Lorentz force gradually loses its stability with increasing particle. All these are consequences of having a non-Hermitian open system that possesses exceptional points, the singularities in the vibrational frequency spectrum of the non-Hermitian force constant matrix. Stability can be retained by introducing viscous damping medium, such as water, to take away the energy pumped in by light. Such binding, primarily due to Lorentz force but has to be assisted by damping, may be termed “opto-hydrodynamic binding.” Our non-Hermitian theory is providing novel perspectives and directions for optical binding and other related situations such as acoustic trapping..

We use Raman tweezers (RTs) to manipulate micro and nano-plastics and individual cosmic dust particles. In doing this we are able to identify their compositions and shape, and to study their response to optical forces without any substrate effects. By RTs we can characterise unambiguously single micro and nano-particles, overcoming the standard Raman spectroscopy capabilities, intrinsically limited to ensemble measurements. In particular, RTs allow us to unambiguously discriminate micro and nano-plastics from organic matter and mineral sediments, also in the presence of a thin eco-corona to have a better understanding of the fragmentation processes of plastics in the sea environment. After a brief introduction about RTs we present our experimental results. First, we report the trapping and identification of a broad range of small micro- and nano-plastics in both distilled and sea water, showing unambiguous discrimination between different plastics coming from marine sediments and organic matter. Then, we discuss the Raman spectra of single 3D-trapped fragments of the lunar meteorite DEW 12007. These results demonstrate the great potential of Raman tweezers for space exploration and for the understanding of the fate and distribution of micro- and nano- plastics in the marine environment. We acknowledge funding from the agreement ASI-INAF n.2018-16-HH.0, project “SPACETweezers” and from the MSCA ITN (ETN) project ”Active Matter”.

Upconverting nanoparticles (UCNPs) have been used as optical probes in a great variety of scenarios ranging from cells to animal models. When optically trapped, a single UCNP can be remotely manipulated making possible, for instance, thermal scanning in the surroundings of a living cell. When conventional optics is used, the stability of an optically trapped UCNP is very limited. Its reduced size leads to optical potentials comparable to thermal energy, and up to now, stable optical trapping of a UCNP has been demonstrated only close to room temperature. This fact limits their use above room temperature, for instance, the use to investigate protein denaturalization that occurs in the 40–50 °C range. In this work, stable optical trapping of a single UCNP in the 20–90 °C range has been demonstrated by using a photonic nanojet. The use of an optically trapped microsphere makes it possible to overcome the diffraction limit producing another optical trap of smaller size and enhanced strength. This simple strategy leads not only to an improvement in the thermal stability of the optical trap but also to an enhancement of the emission intensity generated by the optically trapped UCNP.

In this talk, I will present our recent work on particle manipulation via the evanescent field of tapered optical fibres or optical nanofibres. Evanescent fields emanating from an optical nanofibre, can exert a transverse radiation force on particles near the fibre surface. We have experimentally demonstrated the light-induced rotation of isotropic, dielectric microparticles around a single-mode optical nanofiber. The rotation frequency is related to the polarisation of the guided light and, as predicted theoretically, the direction of motion is opposite to the flow of energy around the fibre. Recently, we have extended this work to anisotropic particles to explore twisting of the object via the transverse spin.

The invited talk will present recent theoretical proposals and analysis in nonclassical quantum optomechanics with optically levitating nanoparticles and predictions for further experimental development in this direction.

The initial, landmark integrated photonic devices relied on silicon and III-V materials, and recent advances in material fabrication and deposition methods have enabled a plethora of new technologies based on materials with higher optical nonlinearities, including 2D materials and organic polymers. However, nonlinear optical (NLO) organic molecules, which are distinct from macromolecules or polymers, have not experienced similar growth due to a perceived environmental instability and to challenges related to intra and intermolecular interactions. Because NLO small molecules have NLO coefficients that are orders of magnitude larger than conventional optical materials, developing strategies to fabricate optical devices could enable significant performance improvements. In recent work, we combined conventional top-down fabrication methods with bottom-up techniques to develop on-chip optical devices that incorporate NLO optical molecules. These hybrid systems provide access to optical behavior and performance not attainable with conventional material systems. In this seminar, I will discuss a couple examples of NLO small molecule integrated resonators, including Raman lasers and all optically-switchable devices.

The resonant enhancement of both mechanical and optical response in microcavity optomechanical devices allows exquisitely sensitive measurements of stimuli such as acceleration, mass and magnetic fields. For example, ultrasensitive magnetometry has been realized by integrating a magnetostrictive material Terfenol-D into a high Q optical microcavity [1,2]. Here we report a magnetic field sensitivity of 26.5 pT/Hz1/2, which is comparable to that of the similar-sized superconducting quantum interference device (SQUID) based magnetometry, but without using cryogenic cooling [3]. The magnetometers are fabricated through depositing Terfenol-D particles into microcavites. We also developed a scalable and reproducible fabrication pathway for cavity optomechanical magnetometers, through sputter coating a thin film of Terfenol-D into the microcavity (as shown in Fig. 1 left), without degrading the quality factor of the microcavities and the performance of the magnetostrictive material [4]. Furthermore, we also demonstrated that by using squeezed light the noise floor of the magnetometer can be suppressed (as shown in Fig. 1 right), and therefore the sensitivity can be improved [5].

“Cabaret” scheme allows fast and precise simulating of long temporal dynamics of the microcavities with GVD, cross- and self-phase modulation taken into consideration. Proposed scheme and model allow investigating cavity dynamics with two counter-propagating pulse trains with second-order dispersion and modulation instability, Rayleigh scattering and other effects such as Raman and SB Scattering and linear wave coupling as and if required in numerical experiment.

Hybrid photonic systems have tremendous potential as versatile platforms for the study and control of nanoscale light-matter interactions and observation of chemical dynamics since they allow use of a mixture of components contributing high quality factors, low mode volumes, molecular selectivity, and topological protection. Individual metallic nanoparticles deposited on dielectric whispering gallery mode optical microresonators provide an excellent example where ultrahigh-quality optical whispering-gallery modes can be combined with nanoscopic plasmonic mode volumes to maximize the system’s photonic performance. Incorporation of microfluidic elements allows these desirable photonic properties to be deployed to follow chemical reaction dynamics. Topological photonic structures designed to enable use of low index materials allow hybridization with tailorable molecular systems.

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Optical sensors have a large impact in the fields of life science research, drug discovery and medical applications. Thanks to optical measurements techniques, that can provide high sensitivity, compactness, fast response and real-time measurements, optical biosensors are gaining an increasing diffusion. The recent advances in optical microresonators technology have led to the demonstration of the possibility of recognizing single molecules or biological species. In parallel, the advances in nanotechnology and photonics have recently led to a new generation of nanotool sets, capable of probing the single cell: it has been demonstrated that nanobiosensors can detect biochemical targets and proteins inside living single cells. These nanoprobes would also allow us to scan chemical reactions on surfaces or in small domain In this communication we present preliminary results concerning the fabrication and the use of nanoprobes consisting of optical fibers having nanosized tips, such as those which were originally developed for use in near-field optical microscopy. We started to develop a procedure to construct these nanosensors by pulling an optical fiber to a sub-micrometer diameter at the tip, and to subsequently coat its sides with a thin metal layer. In parallel, we choose to use commercially available nanoprobes to proceed with functionalization and biosensing tests. The results, which confirm the potential of these nanotools, will be reported at the conference.

The claim that something + nothing = something new is, viewed from the outside, an audacious one. Nonetheless, this is the claim at the heart of a rapidly emerging field that spans physics, materials science and chemistry. In this overview I will present an introductory perspective to the key physics involved and highlight areas that stretch our imagination. I will include a personal perspective on areas that seem to me to be in need of deeper investigation.

This talk will describe our recent studies of Dicke cooperativity, i.e., many-body enhancement of light-matter interaction, a concept in quantum optics [1]. This enhancement has led to the realization of the ultrastrong coupling (USC) regime, where new phenomena emerge through the breakdown of the rotating wave approximation (RWA) [2]. We will first describe our observation of USC in a 2D electron gas in a high-Q THz cavity in a magnetic field [3], with definitive evidence for the vacuum Bloch-Siegert shift [4], a signature of the breakdown of the RWA. Second, we will present microcavity exciton polaritons in aligned carbon nanotubes [5], exhibiting cooperative USC with continuous controllability over the coupling strength. Finally, we have shown that Dicke cooperativity also occurs in a magnetic solid in the form of matter-matter interaction [6-8]. These results provide a route for understanding, controlling, and predicting novel phases of matter using concepts and tools available in quantum optics. 1. K. Cong et al., J. Opt. Soc. Am. B 33, C80 (2016). 2. P. Forn-Díaz et al., Rev. Mod. Phys. 91, 025005 (2019). 3. Q. Zhang et al., Nat. Phys. 12, 1005 (2016). 4. X. Li et al., Nat. Photon. 12, 324 (2018). 5. W. Gao et al., Nat. Photon. 12, 362 (2018). 6. X. Li et al., Science 361, 794 (2018). 7. M. Bamba et al., arXiv:2007.13263. 8. T. Makihara et al., arxiv.2008.10721.

We present new approaches to design and fabricate resonant nano-cavities and manipulate plasmons and phonon-polaritons in the technologically important mid-infrared spectral range. We have developed a technique called atomic-layer lithography to produce gold coaxial ring cavities exhibiting the effective epsilon-near-zero (ENZ) effect. Here we use ENZ nanocavities filled with a model polar medium (SiO2) to demonstrate ultrastrong coupling between polar phonons and gap plasmons. Next, we describe a new device structure – ‘image polariton’ resonator’ – that can be coupled with graphene, boron nitride, or other 2D materials to launch and harness ultraconfined high-momenta polaritons with high coupling efficiency. Potential applications of these engineered nanocavities include infrared sensing, molecular fingerprinting, photodetection, nonlinear optics, and on-chip waveguide integration.

Recent experiments demonstrate the control of chemical reactivities by coupling molecules inside an optical microcavity. In contrast, transition state theory predicts no change of the reaction barrier height during this process. Here, we present a theoretical explanation of the cavity modification of the ground state reactivity in the vibrational strong coupling (VSC) regime in polariton chemistry. Our theoretical results suggest that the VSC kinetics modification is originated from the non-Markovian dynamics of the cavity radiation mode that couples to the molecule, leading to the dynamical caging effect of the reaction coordinate and the suppression of reaction rate constant for a specific range of photon frequency close to the barrier frequency. We use a simple analytical non-Markovian rate theory to describe a single molecular system coupled to a cavity mode. We demonstrate the accuracy of the rate theory by performing direct numerical calculations of the transmission coefficients with the same model of the molecule-cavity hybrid system. Our simulations and analytical theory provide a plausible explanation of the photon frequency dependent modification of the chemical reactivities in the VSC polariton chemistry.

An essential area of nanophotonics is the creation of efficient quantum emitters operating at high frequencies. In this regard, plasmon nanoantennas based on nanoparticles on metal (nanopatch antennas) are incredibly relevant. We have created and investigated a new hybrid nanoantenna with a cube on metal and quantum emitters. We demonstrate an increase up to 60 times for the rate of spontaneous emission. The results show the possibility of creating plasmon antennas in a controlled way by creating an array of regularly arranged nanoscale cavities-resonators.

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Robotic swarms recently rendered as a versatile and affordable alternative to traditional microscale platforms for experimental studies of non-equilibrium active matter consisting of self-propelled or self-rotating particles. In the present paper, we develop and experimentally realize a swarm of self-rotating bristle-bots suitable for a wide range of experimental active matter studies. Optimizing bristle-bot design to emulate different side friction between individual robots, we study the dynamics of such swarms focusing our attention on the jamming transition.

Recent advances in 3D printing, lithography and computational design have spurred rapid progress in the development of passive metamaterials. By interweaving simple subunits in intricate geometric arrangements, metamaterials can be custom designed to have many remarkable response features, from acoustic and photonic band gaps to auxetic behavior and topological robustness. In parallel, the last few years have seen the introduction of new classes of artificial and bio-inspired active materials based on colloidal and microbial suspensions or internally actuated gels. These non-equilibrium systems show great promise as components in autonomous soft robotic and microfluidic devices, and have reached a level of understanding where these applications can now be fruitfully developed. In this talk, I will discuss our recent work that aims to implement a computational framework for the inverse design [1] of discrete active metamaterials. Building a network-based description, we will illustrate how optimized material structures can be used to harvest energy from correlated fluctuations [2,3], and outline basic design principles for active topolectrical circuits [4,5]. [1] Ronellenfitsch et al., Phys. Rev Mat. 3: 095201 (2019) [2] Ronellenfitsch et al., Phys. Rev. Lett. 121: 208301 (2018) [3] Woodhouse et al., Phys. Rev. Lett. 121: 178001 (2018) [4] Kotwal et al., arXiv:1903.10130 [5] Ronellenfitsch and Dunkel, arXiv:2003.09634

We use robotic metamaterials to probe a wide range of non-Hermitian phenomena in mechanics. Specifically, by combining non-reciprocal gain and non-Hermitian topology, we create materials with unidirectional (nonlinear) waves and unusual responses to impacts.

Active systems are not constrained by the principle of energy conservation, allowing for a wide variety of wave phenomena not accessible to ordinary passive matter. By implementing local non-conservative interactions between particles within a network, complex collective behavior can result, providing new avenues in material design. In particular, active elastic materials can be made by considering Hookean couplings which depend on the actuation direction, breaking chiral symmetry. A corollary of this non-reciprocity is that the work around a closed loop of deformations is generally nonzero.  To probe this departure from classical elasticity, I consider a simple building block made from robotic units equipped with sensors and actuators, exhibiting work cycles without external driving, i.e. due to self-oscillation. Chains of these robotic units demonstrate interesting functionalities such as locomotion and impact control when coupled to the environment by leveraging the uni-directional waves that propagate through it. Furthermore, a 2D lattice with embedded active rings exhibits odd elastic properties as well as non-Hermitian skin waves showcasing a relationship between microscopic couplings and macroscopic properties. Altogether, these systems of distributed robots represent an ideal platform to study, engineer and control the emergent properties of active systems facilitating the development of autogenous smart materials, topological sensors and noise suppression schemes.

As tiny robots become individually more sophisticated, and larger robots easier to mass produce, a breakdown of conventional disciplinary silos is enabling swarm engineering to be adopted across scales and applications, from nanomedicine to treat cancer, to cm-sized robots for large-scale environmental monitoring. This convergence of capabilities is facilitating the transfer of lessons learned from one scale to the other. Cm-sized robots that work in the 10,000s may operate in a way similar to reaction-diffusion systems at the nanoscale, while sophisticated microrobots may have individual capabilities that allow them to achieve swarm behaviour reminiscent of larger robots with memory and communication. Although the physics of these systems are fundamentally different, much of their emergent swarm behaviour can be abstracted to their ability to move and react to their local environment. This presents an opportunity to build a unified framework for the engineering of swarms across scales that makes use of machine learning to automatically discover suitable agent designs and behaviours, realistic simulators to capture the physics of the agents, and general performance measures based on emergence. Such a framework would push the envelope of what swarm robotics is currently used for, bringing together active matter physics, collective behaviour research, synthetic biology and medicine towards the desire to engineer useful swarms.

The field of plasmonics in recent years has experienced a certain shift in priorities. Faced with undisputable fact that loss in metal structures cannot be avoided, or even mitigated (at least not in the optical and near IR range) the community has its attention to the applications where the loss may not be an obstacle, and, in fact, can be put into productive use. Such applications include photo-detection, photo-catalysis, and others where the energy of plasmons is expended on generation of hot carriers in the metal. Hot carriers are characterized by short lifetimes, hence it is important to understand thoroughly their generation, transport, and relaxation in order to ascertain viability of the many proposed schemes involving them. In this talk we shall investigate the genesis of hot carriers in metals by investigating rigorously and within the same quantum framework all four principle mechanisms responsible for their generation: interband transitions, phonon-and-defect assisted intraband processes, carrier-carrier scattering assisted transitions and Landau damping. For all of these mechanisms we evaluate generation rates as well as the energy (effective temperature) and momenta (directions of propagation) of the generated hot electrons and holes. We show that as the energy of the incoming photons increases towards the visible range the electron-electron scattering assisted absorption becomes important with dire consequences for the prospective “hot electron” devices as four carriers generated in the process of the absorption of a single photon can at best be characterized as “lukewarm” or “tepid” as their kinetic energies may be too small to overcome the potential barrier at the metal boundary. Similarly, as the photon energy shifts further towards blue the interband absorption becomes the dominant mechanism and the holes generated in the d-shell of the metal can at best be characterized as “frigid” due to their low velocity. It is the Landau damping process occurring in the metal particles that are smaller than 10nm that is the most favorable on for production of truly “hot” carriers that are actually directed towards the metal interface. We also investigate the relaxation processes causing rapid cooling of carriers. Based on our analysis we make predictions about performance characteristics of various proposed plasmonic devices.

A surface plasmon in a metal nanoparticle is the coherent oscillation of the conduction band electrons leading to both absorption and scattering as well as strong local electromagnetic fields. These fundamental properties have been exploited in many different ways, including surface enhanced spectroscopy and sensing, photothermal cancer therapy, and color display generation. Chemical synthesis and assembly of nanostructures are able to tailor plasmonic properties that are, however, typically broadened by ensemble averaging. Single particle spectroscopy together with correlated imaging is capable of removing heterogeneity in size, shape, and assembly geometry and furthermore allows one to separate absorption and scattering contributions. In this talk I will discuss our recent work on distinguishing the different contributions that cause plasmon decay, and especially plasmon damping due to energy and charge transfer from the metal to molecular, semiconducting, and metallic acceptors.

In recent years, it has been found that noble metal nanoparticles catalyze chemical reactions when their plasmon resonances are excited by light radiation. Typically, the explanation for these novel phenomena is focused on hot electrons generated by plasmonic excitation. I will talk about the oft-missing piece in the story: holes. In gold nanoparticles, in particular, due to a unique electronic structure and strong special relativistic effects, the photoexcitation of plasmon resonances leads to the generation of energetic d-band holes along with sp-band electrons. These electron–hole pairs can be utilized as highly reactive reagents in redox chemical reactions. A striking example of this phenomenon is the multielectron conversion and C–C coupling of CO2 to form hydrocarbons on gold nanoparticles under visible light. I will also describe an example of photoexcitation modifying catalytic selectivity and another where it drives a thermodynamically uphill reaction enabling free energy to be harvested from light and stored in the form of energy-rich bonds.

The sustainability of the future energy grid depends on the ability to discover new and more efficient processes that enable the storage of solar energy in the form of chemical bonds through the production of solar fuels and chemicals. In this scenario, plasmonic nanostructures and metamaterials represent a primary choice to enhance light-matter interaction and favor energy storage with high efficiency. However, plasmonic materials for practical and scalable applications must show optimized hot carrier/heat generation, abundance on the earth's crust, high-temperature stability, chemical stability, and compatibility with device/material processing. Plasmonic metal nitrides feature many of these properties holding promises for the fabrication of scalable devices. In this contribution, I will present the use of plasmonic metal nitrides in various solar-driven chemical processes discussing the fundamental mechanisms involving hot carriers and/or local heating utilization.

Recently, we have shown [Dubi, Un & Sivan, Chem. Sci., 2020] that plasmonic heating effects play a crucial role in enhancing the rate of bond-dissociation reactions. This was done by applying the temperature-shifted Arrhenius Law to the experimental data, detailed analysis of the heat generation occurring within the relevant catalyst samples, and identification of experimental errors in the temperature measurements. This result was corroborated with the complete calculation of the steady-state electron non-equilibrium in the metal [Dubi & Sivan, Light: Sci. Appl. (2019)], a consequent Fermi golden-rule argument [Sivan, Un, & Dubi, Faraday Discuss. (2019)] that implied on the unlikeliness of nonthermal electrons to cause the catalysis. In this work [Un & Sivan, ACS photonics, 2021], we present three important extensions to our previous studies. First, we analyze thermal effects in reduction-oxidation reactions, where charge transfer is an integral part of the reaction. Second, we analyze not only the spatial distribution of the temperature but also its temporal dynamics. Third, we also model the fluid convection and stirring. We further analyze two exemplary experimental studies and show that thermal effects can explain the experimental data in one of the experiments [Huang et al., Faraday Discuss. (2019)], but not in the other [Yu & Jain, Nat. Commun. (2019)]. This shows that redox reactions are not necessarily driven by non-thermal charge carriers.

We study emerging ordered quantum phases of ultracold spinor quantum particles in multimode cavities to synthesize dynamic gauge fields, spin orbit coupling, or long range spin interactions. Quantum particles coupled to field modes of optical resonators hybridize with cavity photons, which collectively couple spin and motional dynamics. By help of multiple polarization modes one is able to engineer spin-dependent dynamic optical potentials and tailored long-range density and spin-spin interactions towards a versatile analogue quantum simulator. The emerging spin-and-density-ordered complex quantum phases can often be characterized in situ via properties of the cavity output spectra. For larger interaction strength the light induced long range coupling of the particles can induce regular crystallization of the particles bound by light and the appearance of new exotic quantum phases with short and long range order as found in a supersolid. The system also offers unique properties as a future general purpose quantum simulator. Refs: F. Mivehvar, F. Piazza, T. Donner, H. Ritsch, Cavity QED with Quantum Gases: New Paradigms in Many-Body Physics, arXiv preprint arXiv:2102.04473, 2021 H. Ritsch, P. Domokos, F. Brenneke and T. Esslinger, Cold atoms in cavity-generated dynamical optical potentials, REV. MOD. PHYS. 85, 553, 2013

We studied the Fourier spectrum of the light-scattering profiles of single particles in the Rayleigh-Gans-Debye and Wentzel–Kramers–Brillouin approximations. In the case of a homogeneous sphere, we connected the key parameters of the spectrum and the sphere characteristics. Based on these results, in the framework of Lorentz–Mie theory, we have improved the existing spectral characterization method for spheres for higher refractive indexes.

The possibility to exploit the interaction between molecular vibrations and localized plasmons in nanoscale cavities has set a new regime of optomechanics, where near-strong optomechanical coupling has been identified in surface-enhanced Raman spectroscopy (SERS) of organic molecules. The use of light localized onto atomic protrusions in metallic cavities produces extremely small effective mode volumes, down to the atomic scale, in the so-called picocavities. To capture the complexity of modes of the plasmonic nanocavity, we develop a full continuum-field model based on the description of the nanocavity Green’s function, which serves to describe the optomechanical interactions more accurately, beyond the single optical mode approximation. Within this molecular optomechanics context, we identify and theoretically describe strong nonlinearities of the Stokes and anti-Stokes photons emitted from nano- and pico-cavities as a function of incident laser intensity. Moreover, a shift of the frequencies of the molecular vibrational fingerprints, analog to the optical spring effect in standard optomechanics is also identified, and experimentally validated by analyzing the Raman signal from molecules in such nanocavities. Finally, collective effects, where the vibrations of different molecules coherently couple to each other building up a bright collective vibrational supermode, are also explored to quantitatively explain the Stokes signal from molecular self-assemblies. Molecular optomechanics enables a new regime of interactions between cavity photons and mechanical vibrations at room temperature, which could be used to control molecular reactivity on demand, and exploit vibrational states of matter for quantum technology applications.

Mechanical systems represent a fundamental building block in many areas of science and technology, from atomic-scale force sensing to quantum information transduction to kilometer-scale detection of infinitesimal spacetime distortions. All such applications benefit from improved readout sensitivity, and many seek new types of mechanical actuation. In this talk I will discuss our efforts to realize a tabletop, room-temperature optomechanical system capable of sensing the broadband (100Hz - 1MHz) quantum noise in the radiation force from incident laser light; this would represent a milestone toward optomechanically tuned squeezed light sources and mechanical sensitivities beyond the standard quantum limit. I will also discuss our progress toward creating a qualitatively different kind of optomechanical system in which light strongly tunes the spatial extent and effective mass of a mechanical mode.

The ability of photonic metasurfaces to steer and bend light is uniquely beneficial for the control of radiation pressure over macroscale areas. We discuss the principles, challenges, and opportunities in optical manipulation enabled by the ability to locally tailor optical forces and torques at each point on the object surface. The need to account for both the optical and the mechanical properties in a single object leads to unique design figures of merit, and we present design approaches that can inform optimal metasurface structures based on the target manipulation application. The possibilities for novel long-range levitation and actuation mechanisms will be discussed.

Hybrid quantum devices, incorporating both atoms and photons, are able to exploit the benefits of both systems. Compact, robust atom-photon interfaces will enable scalable architectures for quantum computing and quantum communication, as well as chip-scale sensors and single-photon sources. We demonstrate a new type of interface and show the interaction of cold cesium atoms with resonant photons. For this atoms are cooled in a magneto-optical trap, transferred to an optical dipole trap and positioned inside a transverse, 30 µm diameter through-hole in an optical fibre, created via laser micromachining. We trap about 300 atoms at a temperature of 120µK. When the guided light is on resonance with the caesium D2 line, up to 87% of it is absorbed by the atoms. Our technique should be equally effective in optical waveguide chips and other existing photonic systems. We also discuss the influence of hole shapes on transmission and prospects of adding a micro-cavity.

Non-reciprocal elements are key components for fiber-optical networks and integrated optical chips. For example, they allow one to protect lasers from harmful optical feedback and to implement optical add-drop multiplexers or cascaded quantum systems. A novel class of such non-reciprocal elements utilizes the internal spin of quantum emitters in order to break Lorentz reciprocity. While respective isolators and circulators have been demonstrated recently, a corresponding non-reciprocal amplifier is hitherto missing. Here, we experimentally show non-reciprocal Raman amplification of light pulses using spin-polarized atoms that are chirally coupled to an optical nanofiber. We control the direction in which amplification occurs via the Zeeman state in which the atoms are prepared. We investigate the dependence of the optical output power on the number of atoms and obtain over 40 % single-pass gain for about 2000 atoms. In addition, we show that non-reciprocal amplification prevails in the absence of an offset magnetic field. Our results can be readily transferred to other types of nanophotonic waveguides and suitable quantum emitters.

We present in this work a non-destructive and non-invasive imaging spectroscopic technique with a high spatial and spectral resolution to characterize the light propagation behavior along a centimetric length and nanoometric size tapered optical fiber in operation.

We study the optical properties of an array of atomic emitters weakly coupled to the guided optical modes of a waveguide and coherently driven by a plane wave. Remarkably, the collective scattering rate into the guided modes reaches a maximum when the array is driven at angles different from the geometric Bragg angle and at non-zero detunings of the laser from the atomic resonance. We find an analytical expression for this modified Bragg condition, and show that it arises from the dispersive interactions of the guided light with other coupled atoms. We analytically reveal different scalings of the scattering rate into the guided mode with the number of atoms: Depending on the parameter regime, it can be linear, quadratic, oscillatory, or a constant rate. Surprisingly, however, a symmetric or asymmetric emitter--waveguide coupling does not make a difference for the scaling. The described effects are robust against voids in the atomic array, facilitating an easier experimental observation. Our work sheds new light on Bragg and collective scattering, with implications reaching beyond the optical domain.

We demonstrate both theoretically and experimentally the record-high efficiencies for the coupling of light into the fundamental mode of a step-index optical fiber at almost grazing incidence via the inclusion of axial-symmetric all-dielectric nanostructures on fiber tip. Our results exhibit percent-level of the in-coupling efficiency at angles as large as 80 degrees outperforming fibers with plasmonic metasurfaces and unstructured end faces by several orders of magnitude.

In the last decade, there has been significant interest in investigating light fields confined to the micro- or nanoscale and one platform of particular interest to the atomic physics community is the optical nanofiber (ONF). The evanescent light field, which extends from the fibre surface, is tightly confined in the radial direction and can be very intense while also having a very steep field gradient. Interactions between atoms and such fields have been used for demonstrations of nonlinear processes at very low powers [1], for example. Recent advances in controlling the polarisation of light in the evanescent field [2] has opened new avenues of research in atomic physics using ONFs, including a study on electric quadrupole transitions [3]. Recently, we have exploited the intense evanescent field feature in order to generate cold Rydberg atoms at submicron distances from the surface of an ONF embedded in a cloud of laser-cooled Rb-87 atoms [4]. A ladder-type, two-photon excitation scheme was used to excite the atoms to the n=29 or 30 Rydberg states and we used a trap loss method to probe the Rydberg excitation. Both coherent two-photon excitation and incoherent two-step excitation were demonstrated. A density matrix-based model was developed for the three-level ladder type system interacting with the evanescent field of the ONF and, despite its simplicity, it explained the main features of our experimental results. Future work on this topic will include incorporating a fibre-based dipole trap for more controlled positioning of the atoms relative to the ONF. Finally, we have developed a theoretical framework for spin selection in monochrome two-photon excitation of alkali atoms as a function of the excitation light’s polarization. We confirm our theory by experimentally probing the 5S_1/2→6S_1/2 transition rate in cold Rb-87 for evanescent field excitation [5]. The transition rate follows a quadratic dependency on the helicity parameter linked to the excitation light's polarization. We showed that, for nonparaxial excitation via an optical nanofiber, the two-photon transition is not completely extinguished by varying the light polarization; this is to be expected due to the nonvanishing longitudinal field component, even for circular polarization. References [1] R. Kumar et al., Phys. Rev. A 17, 013026 (2015). [2] G. Tkachenko, F. Lei, and S. Nic Chormaic, J. Opt. 21, 125604 (2019). [3] T. Ray, et al., New J. Phys. 22, 062001 (2020). [4] K. S. Rajasree et al., Phys. Rev. Res. 2, 012038(R) (2020). [5] K. S. Rajasree et al., Phys. Rev. Res. 2, 033341 (2020).

We report on the observation of collective superstrong coupling of a small ensemble of atoms interacting with the field of a 30–m long fiber resonator containing a nanofiber section. The collective light–matter coupling strength exceeds the free spectral range and the atoms couple to consecutive longitudinal resonator modes. The measured transmission spectra of the coupled atom–resonator system provide evidence of this regime, realized with a few hundred atoms with an intrinsic single-atom cooperativity of 0.13. Moreover, we reveal that the measured resonator spectra exhibit features which are not captured by the Jaynes-Cummings model. Instead, an approach based on the successive interaction of the resonator field with each atom, in a real-space, waveguide formalism, is introduced. Our experimental and theoretical findings are relevant for the rapidly evolving field of study of emitters coupled to waveguides and resonators with strong quantum non-linearities and novel dynamics.

Over the past two decades, graphene has attracted a great deal of attention due to its extraordinary properties. When these properties are translated into applications graphene could have a large impact in various industries and markets such as telecommunications, healthcare, automotive, etc. However, for this to occur there are many milestones that have to be achieved such as graphene manufacturing (growth and transfer) and device fabrication at relevant wafer scales, before moving to component fabrication and system integration into the final product. Graphene’s electronic and mechanical properties make it an ideal candidate to be applied in various types of sensors. The sensors’ market is extremely large since we are dealing with the automotive, electronics and healthcare industries among others. Therefore, it is an excellent starting platform for graphene applications. For example, the current COVID-19 pandemic has demonstrated the urgent need for fast diagnostics in order to minimise and control its effects, here, biosensors based on graphene field effect transistors (GFETs) have shown great potential as a platform for future diagnostics. During this talk, I will cover the fabrication of graphene at wafer scale and the use of graphene in various types of sensors.

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Rapid progress in electrically controlled plasmonics in solids poses a question about possible effects of electronic reservoirs on the properties of plasmons. We find that plasmons in electronically open systems [i.e., in (semi)conductors connected to leads] are prone to an additional damping due to charge carrier penetration into contacts and subsequent thermalization. We develop a theory of such lead-induced damping based on the kinetic equation with microscopic boundary conditions at the interfaces, followed by perturbation theory with respect to transport nonlocality. The lifetime of the plasmon in an electronically open ballistic system appears to be finite, of the order of conductor length divided by carrier Fermi velocity. The reflection loss of the plasmon incident on the contact of the semiconductor and perfectly conducting metal also appears to be finite, of the order of Fermi velocity divided by wave phase velocity. Recent experiments on plasmon-assisted photodetection [Nat. Commun. 9, 5392 (2018)] are discussed in light of the proposed lead-induced damping phenomenon.

In this paper, we consider the effect of charge carrier drift on the absorption/amplification spectrum of THz radiation in a Dirac liquid of graphene with a shifted Fermi level. The absorption/amplification spectra of THz radiation in graphene periodically gated by a metal grating are calculated using a self-consistent electromagnetic approach and the hydrodynamic description of the electron liquid. The response of the structure is described by the nonlocal complex dynamic graphene conductivity obtained taking into account the pressure of the electron liquid, the constant electric field in graphene, and the adiabatic process of the wave propagation. The regimes of absorption/amplification of THz radiation are calculated depending on the magnitude of the direct electric current flowing in graphene. The amplification of THz radiation in graphene with large dissipative losses (with a phenomenological momentum scattering rate of charge carriers of 10^13 1/s) starts for small values of the electron drift velocity.

The operation of a photodetector based on CVD graphene in the wavelength range of 6-10 microns has been investigated. It is shown that the mechanism of photovoltage generation is thermoelectric. The measured response rate was 1 μs, and it was shown that it was limited by the RC-constant of the device and the the laser modultion rate, and not by the photogeneration mechanism. It is shown that the detector is polarization-sensitive and the essence of this phenomenon is clarified.

Weak plasmon modes in periodic structures with a two-dimensional electron gas without an inversion center are studied theoretically. The asymmetry of the electric field and Fourier harmonics of weak plasmon modes can lead to the excitation of a traveling plasmon by an electromagnetic wave normally incident on the structure and to the appearance of nonlinear effects leading to the rectification of the incident radiation. The low radiation damping of weak plasmon modes can be used to increase the efficiency of terahertz plasmon amplifiers.

The classification of topological insulators predicts the existence of high-dimensional topological phases that cannot occur in real materials, as these are limited to three or fewer spatial dimensions. In this talk, I will introduce the physics of four-dimensional (4D) topological lattices, before presenting the results of an electrical-circuit implementation of a 4D topological insulator, in which the lattice dimensionality is established by circuit connections. On the lattice’s three-dimensional surface, we observe topological surface states that are associated with a nonzero second Chern number but vanishing first Chern numbers. Finally, I will present theoretical results for how the phenomenology of superfluid vortices can be extended into 4D, opening the way towards interacting topological systems in higher dimensions.

Bloch oscillations (BOs) are a fundamental phenomenon by which a wave packet undergoes a periodic motion in a lattice when subjected to a force. Observed in a wide range of synthetic systems, BOs are intrinsically related to geometric and topological properties of the underlying band structure. This has established BOs as a prominent tool for the detection of Berry-phase effects, including those described by non-Abelian gauge fields. In this work, we unveil a unique topological effect that manifests in the BOs of higher-order topological insulators through the interplay of non-Abelian Berry curvature and quantized Wilson loops. It is characterized by an oscillating Hall drift synchronized with a topologically-protected inter-band beating and a multiplied Bloch period. We elucidate that the origin of this synchronization mechanism relies on the periodic quantum dynamics of Wannier centers. Our work paves the way to the experimental detection of non-Abelian topological properties through the measurement of Berry phases and center-of-mass displacements.

Recently, inspired by the idea of quantum simulation, there has been a growing interest of exploiting synthetic magnetic fields to control the dynamics of uncharged particles. Quantum properties emerge due to the phase acquired by the particle wave function as it performs a loop around a spatial region containing a synthetic magnetic flux: the Aharonov-Bohm (AB) phase. For certain lattice geometries and specific values of the field, AB caging can be achieved due to the wavefunction destructive interferences. This phenomenon, different with respect to disorder induced localization, arises due to the interplay between the lattice geometry and the magnetic flux and has been predicted and verified in several photonic structures. Here we study AB cages in waveguides arrays of interconnected plaquettes threaded by two synthetic fluxes. With respect to previous proposals, we show that the presence of three arms per plaquette allows to obtain different regimes where all the energy bands became non-dispersive flat. The destructive interference of waves propagating along the three arms allows to tune the caging by changing the tunnel couplings. This reflects on the diffraction pattern allowing to establish a connection between the gauge fields, the lattice topology and the resulting AB interference. The presence of two fluxes allows us to investigate in a simple but non-trivial framework AB caging features, highlighting its topological significance and showing how in this case the effect becomes fully tunable. The novelty and substantial impact of our work lies in a new route to control the dynamics of light localization.

In recent years there has been a flurry of interest in topological materials and in their exotic physics. Most of the developments in optics have been inspired in one way or other by the theory of condensed matter systems. However, photonic systems have a few peculiar features that are not found in their electronic counterparts. The first of such properties is related to the unavoidable material dispersion as the permittivity tensor necessarily depends on frequency. The second property is the particle-hole symmetry inherited from the reality of the electromagnetic field: the spectrum is formed by positive and negative frequencies. In this talk, we will show how the combination of the two properties leads to surprising situations and discuss how they tailor the topology of dispersive photonic platforms. In particular, we will present first principles calculations of the topological numbers of dispersive photonic crystals.

Topological photonics uncovers an entire plethora of remarkable functionalities related to disorder-robust generation, localization and propagation of light flows. While the initial progress in topological photonics was largely inspired by the analogies with condensed matter physics, photonic platforms feature a number of distinctive features, in particular, long-range electromagnetic interactions of the constituent elements. In many cases, this circumstance renders the traditional tight-binding models insufficient to describe physics underlying photonic topological states. In this talk, I will overview a series of our recent works exploring the role of long-range coupling in the formation of topological phases. In particular, the interaction of the next-nearest neighbors may enable new types of corner states splitting them from the band of edge-localized states in photonic kagome lattices [1] (Fig. 1a). Alternatively, such interactions may cause the opening of photonic topological bandgap pulling corner-localized states out of the continuum of the bulk modes for D4-symmetric models [2] (Fig. 1b). Furthermore, coupling of the distant neighbors becomes especially critical in the three-dimensional case enabling symmetry-protected higher-order topological insulator based on the three-dimensional Su-Schrieffer-Heeger model hosting zero-dimensional corner-localized topological state (Fig. 1c).

Topological photonics provides a fundamental framework for robust manipulation of light, including directional transport and localization with built-in immunity to disorder. Combined with an optical gain, active topological cavities hold special promise for a design of light-emitting devices. In our work, we design trapped topological modes with singular emission profiles in nanopatterned InGaAsP membranes. The pattern geometry is created by stitching three off-set sectors of Kekule graphene lattices. Simulations reveal high-quality mid-gap states bound to the core of the structure and hosted in the 100nm-width band gap at the wavelength of about 1500 nm. The far-field radiation pattern has pronounced vortex features with a singularity at the normal direction. Such trapped modes are analogous to the zero-mode solutions of the Dirac equation with a mass vortex, first described by Jackiw and Rossi. Our sectorial implementation can be applied for engineering a network of coupled topological states. As an example, we consider a dimer of two core-bound states and demonstrate a PT-phase transition by controlling distribution of the optical gain and coupling strength. The system is described by the non-Hermitian coupled-mode equations including the terms quantifying for spatial mode overlapping and coupling through the radiation continuum.

Engineering robust solid-state quantum systems is amongst the most pressing challenges to realize scalable quantum photonic circuitry. While several 3D systems (such as diamond or silicon carbide) have been thoroughly studied, solid state emitters in two dimensional (2D) materials are still in their infancy. In this presentation I will discuss single defects in an emerging 2D material – hexagonal boron nitride (hBN) that as promising qubits for quantum photonic applications. In particular, I will focus on ways to engineer these defects deterministically using either chemical vapour deposition growth or ion implantaiton, and show results on strain tuning of these ultra bright quantum emitters. I will then highlight promising avenues to integrate the single defects with photonic cavities, as a first step towards integrated quantum photonics with 2D materials. I will summarize by outlining challenges and promising directions in the field of quantum emitters and nanophotonics with 2D materials.

Periodic structures whose periods are comparable or smaller than the wavelength act as effective media not only for electromagnetic waves but also for heat conduction. By fabricating high aspect ratio nanostructures with titanium nitride and silicon and performing photothermal heating experiments with a Raman spectroscopy setup, we show that those structures have high optical absorption and low thermal conductivities in which the latter are caused by the extreme thermal anisotropy. A simple effective medium approximation which takes into account the periodic nature works well in estimating the effective thermal conductivity. Our strategy can be applied to other materials and structures where high optical absorption and low thermal conductivity are required.

Here, we report on a new approach behind plasmon-assisted optical heating for spectroscopically recognizing the glass transition temperature of spatially confined poly-methylmethacrylate polymers spin-coated on a thermoplasmonic metasurface consisting of an array of square-shaped titanium nitride pads on a c-Si substrate. A local photo-heating is controlled through Raman thermometry of the c-Si substrate that functions as a temperature-sensing Raman reporter. We show that optical heating can be controlled by extruding the c-Si substrate. Anomalous optical heating in titanium oxynitrides pads, exhibiting a double epsilon-near-zero behavior, is reported. The developed method will allow one to locally probe not only 2D structural glass transitions of heterogeneous glassy polymers and polymeric blends, but 3D confined polymers as well.

In the talk, I will cover recent advances in the field of optical heating of resonant all-dielectric nanostructures [1] with temperature-sensitive Raman scattering feedback [2]. Such efficient laser heating in all-dielectric structures is very promising for bio-applications [3], including cancer therapy [4], photothermally-induced phase transitions [5], and reshaping of metasurfaces [6], and tuning of nonlinear (SHG) optical response due to thermooptical effect [7]. [1] Zograf, G. P., Petrov, M. I., Makarov, S. V., & Kivshar, Y. S. (2021). All-dielectric thermonanophotonics. Advances in Optics and Photonics (Accepted) https://arxiv.org/abs/2104.01964 [2] Zograf, G. P., Petrov, M. I., Zuev, D. A., Dmitriev, P. A., Milichko, V. A., Makarov, S. V., & Belov, P. A. (2017). Resonant nonplasmonic nanoparticles for efficient temperature-feedback optical heating. Nano letters, 17(5), 2945-2952. [3] Milichko, V. A., Zuev, D. A., Baranov, D. G., Zograf, G. P., Volodina, K., Krasilin, A. A., ... & Belov, P. A. (2018). Metal‐dielectric nanocavity for real‐time tracing molecular events with temperature feedback. Laser & Photonics Reviews, 12(1), 1700227. [4] Zograf, G. P., Timin, A. S., Muslimov, A. R., Shishkin, I. I., Nominé, A., Ghanbaja, J., ... & Makarov, S. V. (2020). All‐optical nanoscale heating and thermometry with resonant dielectric nanoparticles for controllable drug release in living cells. Laser & Photonics Reviews, 14(3), 1900082. [5] Zograf, G. P., Yu, Y. F., Baryshnikova, K. V., Kuznetsov, A. I., & Makarov, S. V. (2018). Local crystallization of a resonant amorphous silicon nanoparticle for the implementation of optical nanothermometry. JETP Letters, 107(11), 699-704. [6] Aouassa, M., Mitsai, E., Syubaev, S., Pavlov, D., Zhizhchenko, A., Jadli, I., ... & Kuchmizhak, A. (2017). Temperature-feedback direct laser reshaping of silicon nanostructures. Applied Physics Letters, 111(24), 243103. [7] Pashina, O., Frizyuk, K., Zograf, G., and Petrov, M., (2021) (In prep.)

In the recent years, semiconductor and dielectric nanophotonic structures attracted a lot of attention for their resonant optical properties finding applications in thermal tuning and optical heating. Exciting high quality optical modes of both electric and magnetic nature in nanoresonators of high-index materials, one can effectively enhance optical absorption in such structures. Another big advantage of semiconductor materials is the ability to finely control the level of optical losses in visible and near infrared (near-IR) range through varying the doping level. In this work, we show theoretically that by moderate carrier doping of silicon via donors from group V materials one can achieve effective heating of nanoresonators. We show that by tuning the doping level of crystalline silicon supporting high quality non-radiative modes based on quasi bound states in the continuum one can achieve strong heating in near-IR under continuous wave regime illumination. We believe that our finding will pave the way for an efficient semiconductor near-IR all-optical sensors and nanoheaters.

Conversion of light to heat in nanostructures plays a crucial role for many applications, including photothermal therapy, thermophotovoltaics, photocatalysis, heat assisted magnetic recording and photodetection. The efficiency of optical heating is determined by two factors: (1) the ability to absorb light and (2) thermal properties of the nanostructure and its surrounding. It is well known that light-matter interaction, and in particular absorption, is a weak process. This is due to mismatch between impedances of an absorber/emitter and an electromagnetic wave. Therefore, an enhancement of the absorption strength is required for the efficient optical heating. In general, the amount of the absorbed power depends on the imaginary part of the medium’s permittivity and the magnitude of the optical field within the nanostructure. One of the ways to increase the absorption level is to synthesize novel materials that would have large intrinsic losses, i.e. large imaginary permittivity. On the other hand, one can enhance the field intensity within the nanostructure with respect to the intensity of incident radiation. Over the last decades, several mechanisms of field enhancement have been proposed. These mechanisms utilize resonant structures, such as plasmonic nanostructures, microresonators and all-dielectric antennas. Excitation of plasmonic resonances in metallic structures leads to sub-diffraction localization of light, enabling to increase the local field intensity by several orders of magnitude. Despite considerable progress in thermoplasmonics, this enhancement mechanism in not optimal for optical heating. The reason lies in the fact that the field enhancement occurs mainly outside the volume of a nanostructure. Another approach is based on electromagnetic modes in dielectric structures, such as whispering-gallery-mode resonances and Mie resonances. In this case, the field experience enhancement inside the particle. Using dielectrics with intrinsic losses it is possible to achieve regimes of efficient absorption and heating. In order to excite resonant modes in dielectric antennas their size should be on the order of the wavelength of light. This limitation makes miniaturization of such devices challenging. In this work we propose local optical heaters based on alternative strategy for enhancing of absorption. This strategy leverages optical effects in the class of materials with near-zero permittivity, that has recently attracted a widespread interest [1,2]. Epsilon-near-zero (ENZ) materials, being an intermediary between metals and dielectrics, combine their advantages. ENZ structures are able to enhance optical fields on the nanoscale, while the enhancement occurs within the ENZ media. Hence, this material platform is promising for realization of highly-efficient optical absorbers. Here we synthesize and use titanium oxynitride (TiON) nanocomposites that demonstrate ENZ properties in the visible and near-IR ranges. In contrast to well-established ENZ materials (ITO, AZO, GZO), TiON allows for flexible tuning of their properties – optical (dielectric function) and thermal (heat capacity and conductivity) parameters. For instance, we have shown that by adjusting the synthesis procedure it is possible to achieve a broadband ENZ behavior [3]. In order to maximize the efficiency of photothermal conversion, we study multiphysical effects that occur in our ENZ structures under optical excitation. This includes mutual influence of the optical properties of the material and the temperature of the nanostructure. We experimentally observed that the ENZ wavelength λENZ of TiON can experiences considerable shift at elevated temperatures: for some samples an increase in temperature of 100 degrees leads to a λENZ shift of 50 nm. We also analyze the ENZ effects, such as wavelength expansion and reduced group velocity, and their role in the absorption enhancement. As a result, this allowed us to find optimal parameters of TiON-based ENZ structures for realization of efficient optical heating in the broadband spectral range covering visible and near-infrared. References: [1] N. Kinsey et al. Nat. Rev. Mater. 4, 742-760 (2019). [2] I. Liberal et al. Nat. Photonics. 11, 149-158 (2017). [3] A. V. Kharitonov et al. Opt. Mater. Express. 10, 513-531 (2020).

This talk presents an alternative to spectral signature barcodes for the implementation of chipless-RFID tags. Such chipless-RFID tags are called time-domain signature barcodes, as long as tag reading is carried out in time domain. Specifically, the bits are read sequentially, by proximity, through near field. The tags consist in a linear chain of inclusions (metallic, apertures, dielectric) on a host dielectric substrate (rigid or flexible, including plastic substrates and organic substrates, such as paper). The sensitive part of the reader is a resonator-loaded transmission line, able to detect the presence of tag inclusions when the tags moves (i.e., is displaced) on top of the reader, in close proximity to it. For tag reading, a harmonic signal is generated and injected to the transmission line of the reader. By tag motion over the reader, the inclusions modify the transmission coefficient of the line, thereby generating an amplitude modulation signal at the output port of the line, and this signal contains the information relative to the ID code. Various chipless-RFID systems based on time-domain signature barcodes are discussed in the talk, including systems with chipless-RFID tags based on metallic and dielectric inclusions, and systems where the tags are read synchronously. It is shown that tags with unprecedented data capacity can be implemented, with very good data density. These systems are of special interest in applications such as secure paper or authentication of premium products, where tag reading by proximity is not an issue.

RFID is a very powerful tool for inventory of assets or reading of sensors at a distance and without direct line of sight, and therefore it is becoming a must have in retail and in the industry. Yet it suffers from any radiofrequency wave based technique: scattering and diffraction of waves. These effects severely limit the reliability of RFID, and various solutions have been proposed to tackle this issue, from complex phased arrays to robots or drone assisted RFID systems. Since a few years, we have been developing electronically reconfigurable metasurfaces that, when distributed in a given environment, are able to shape passively in real time and at will the electromagnetic waves emitted by a RFID reader. These can be used to stir the electromagnetic field, resulting in a much more homogeneous distribution over short times, or to control and focus RF energy, both resulting in extremely reliable RFID detection. I will show a few examples of projects we have realized, notably in closed cavity-like systems such as vehicles or cabinets, where the technology achieves tremendous results. Yet this approach based on tunable metasurfaces, because it requires wiring to power the electronics and control it, is very limited to small volumes in terms of integration. Therefore, we have developed an approach based on independent tunable resonators, that can be placed anywhere in a medium and control locally the electromagnetic field without any wire. These wirelessly controlled and energy autonomous resonant unit cells are RFID compatible: they take the energy from the RFID waves to shape them, using instructions coming from the reader. Being extremely low-cost, used at scale and controlled several meters away, they pave the way for ultra-reliable RFID in open systems and large volumes.

Enhancement of electromagnetic signal modulation is one of the key problems formodern contactless communication systems. Using resonance effects allows to achieve significantinteraction between an electromagnetic wave and matter of an antenna, providing opportunityto control scattering. This work demonstrates efficiency of multipole engineering based on Mie theory for dielectric core-shell antennas, particularly we show that generalized Kerker effect isa useful tool for backscattering modulation magnification. Our approach allows to manipulatescattering properties of devices without increasing their size by using all-dieletric concept.

This paper presents a wireless temperature sensor design based on the excitation of a high-Q supercavity mode in a dielectric resonator. Narrow resonance bandwidth improves sensor performance enabling accurate temperature measurements. The sensor consists of a half split ceramic cylinder attached to a metal sheet. The resonator parameters which lead to the excitation of a supercavity mode were obtained numerically. When the ambient temperature increased continuously from 23 to 120°C the notable shift of the resonant frequency was experimentally demonstrated.

I will discuss recent research concerning the control of nanoparticle transport using the evanescent field of the fundamental mode of an optical nanofiber. Challenges posed by the trapping and transport of biological nanoparticles will be discussed, and sophisticated techniques including more selective manipulation will be considered.

In this work, we demonstrate twisting of a probe anisotropic particle due to the transverse spin of light in near field of an optical nanofiber waveguide. The particle is held is elliptically polarized optical tweezers which produce a driving spin by retardation of the light transmitted through the particle. By setting the driving spin angular momentum in the optical tweezers to be parallel or antiparallel with respect to the transverse spin near the nanofiber, we can speed up or slow down the particle’s rotation by about a half of the rotation rate observed without the light in the fiber. We explore the dependence of the optomechanical effect on the propagation direction and polarization of the guided light. In particular, we show that the effect is significant even when the guided light is unpolarized, which seems counterintuitive given that the commonly considered longitudinal spin in such light is zero. Experimental results are supported by semi-analytical and numerical simulations.

Optical sorting of dielectric objects has been developed using holographic optics, nanophotonics, and plasmonics. However, these techniques are limited to the particle selection by the size and refractive index. We propose a technique for optical selection and sorting of nanoparticles according to their quantum mechanical properties. The optical forces reflect these quantum resonant properties of nanoparticles as well as their optical characteristics. The interaction between light and nanomaterials induces not only an energy transfer from photons to the quantum mechanical motion of electrons but also a momentum transfer between them. The change in the photon momentum results in optical forces, which drive the macroscopic mechanical motion of the nanoparticles. Therefore, by monitoring and controlling the particle motions, we realize the characterization and selective manipulation of single nanoparticles having various quantum mechanical properties. We experimentally demonstrated selective transportation of nanodiamonds (NDs) with and without nitrogen-vacancy centers (NVCs). We prepared a tapered optical fiber with ~400-nm diameter, and two laser beams with 532-nm (in resonance of NVC) and 1064-nm (out of resonance of NVC) wavelengths were introduced into the nanofiber from both ends, so that the absorption force can be extracted by balancing the scattering forces. We also propose a methodology for precisely determining the absolute values of absorption cross-sections for single nanoparticles by monitoring the optically driven motion, called as “optical force spectroscopy”. This technique directly and sensitively measures the interaction between light and nanoparticles separately from the scattering effects, based on the photon momentum change and not the energy change.

We present a way for micro-lens and micro-lens array fabrication on the fiber facet by direct laser writing (DLW) method. The proposed setup for DLW printing on the fiber facet can protect objective lens and makes it possible to safely using a wide range of resists. Micro-lens fabricated on the single-mode optical fiber facet is demonstrated. Based on lens-on-fiber system we proposed concept of the micro-lenses on baseplate array printed on the multi-core fiber, where each lens is rigidly aligned with the core. One of the possible micro-lenses on the baseplate array is presented and its optical properties such as focal spot size and resolution are investigated. The possible application of the proposed micro-lens array is complex optical elements, such as micro-objectives with optimized optical design. Moreover, suggested freeform lens array can find application in high-accuracy wavefront sensing.

Owing to their favorable properties including tight optical confinement, strong evanescent fields and evident surface field enhancement, optical micro/nanofibers (MNFs) can offer advantages such as enhanced light-matter interaction and engineerable group-velocity dispersion for nonlinear optical applications. So far various nonlinear effects in optical MNFs, including harmonic generation, four-wave mixing, and supercontinuum generation, have been investigated. However, almost all these effects are obtained using short pulses. Here we demonstrate harmonic generation in optical MNFs pumped with W-level continuous-wave (CW) light at 1550-nm wavelength. Relying on the precise diameter control and long waist length of MNFs, the phase matching condition in the nonlinear optical process can be readily satisfied, and thus evident second harmonic generation (SHG) and third harmonic generation (THG) are observed in MNFs with CW pump.

High-speed tracking of single nano-objects is a pathway to understanding physical, chemical, and biological processes at the nanoscale which is highly relevant in fields such as bio-analytics or medicine. Here we will present our recent results on tracking single or ensembles of nano-objects inside optofluidic microstructured optical fibers via elastic light scattering. Conceptually the nano-objects (plasmonic nanospheres, artificial polymer beads, viruses or phages) are dissolved in a liquid environment inside a well-selected channel of a microstructured optical fiber. Light from the propagating mode scatters off at the diffusing nano-object and is detected transversely via a microscope. Via a statistical analysis of the trajectory of the nano-objects information on its diffusion properties as well as on its diameter are obtained for each particle individually with high accuracy. During this presentation, we will present the fundamentals and details of this sensing approach and focus on selected results achieved in our group. Specifically, we will show the retrieval of the full 3D trajectory of a diffusing nano-sphere using light scattering at an evanescent field in a modified step index fiber that includes a central glass core with a parallel-running micro-channel. We will also report on the simultaneous detection of hundreds of nano-objects in hollow core anti-resonant fibers, allowing to accurately measuring the distribution of the hydrodynamic diameter of an ensemble of gold nano-spheres while the individual nano-object can be labeled by a diameter tag. We will also show first results on measurements of ensembles of inactivated SARS-CoV-2 inside the fibers.

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The ability to extract materials just a few atoms thick has led to the discoveries of graphene, monolayer transition metal dichalcogenides (TMDs), and other important two-dimensional materials. The next step in promoting the understanding and utility of flatland physics is to study the one-dimensional edges of these two-dimensional materials as well as to control the edge-plane ratio. Edges typically exhibit properties that are unique and distinctly different from those of planes and bulk. Thus, controlling the edges would allow the design of materials with combined edge-plane-bulk characteristics and tailored properties, that is, TMD metamaterials. However, the enabling technology to explore such metamaterials with high precision has not yet been developed. Here we report a facile and controllable anisotropic wet etching method that allows scalable fabrication of TMD metamaterials with atomic precision. We show that TMDs can be etched along certain crystallographic axes, such that the obtained edges are nearly atomically sharp and exclusively zigzag-terminated. This results in hexagonal nanostructures of predefined order and complexity, including few-nanometer-thin nanoribbons and nanojunctions. Thus, this method enables future studies of a broad range of TMD metamaterials through atomically precise control of the structure.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are envisaged to play a crucial role as essential building blocks in future high-tech devices. Inherently known from conventional III-V semiconductor alloying is the ability to tune material properties by varying concentrations of constituent atoms in order to realize extended functionality. The price for this tunability is the extra disorder caused by alloying. To unravel the features of the disorder potential in alloys of atomically thin TMDs such as Mo$_{x}$W$_{1-x}$Se$_{2}$, the exciton photoluminescence is measured in a broad temperature range between 10 K and 200 K. In contrast to the binary materials MoSe$_{2}$ and WSe$_{2}$, the ternary system demonstrates non-monotonous temperature dependences of the luminescence Stokes shift and of the luminescence linewidth. Such effects are analogous to those observed previously in conventional III-V and II-VI semiconductors. This behavior is a strong indication of a disorder potential that creates localized states for excitons and affects the exciton dynamics responsible for the observed non-monotonous temperature dependences. A comparison between the experimental data and the results obtained by Monte Carlo computer simulations provides information on the energy scale of the disorder potential and also on the shape of the density of localized states created by the disorder. Statistical spatial fluctuations in the distribution of the chemically different material constituents are revealed to cause the disorder potential responsible for the observed effects in the 2D ternary alloy.

High-refractive-index (Si, Ge, GaP) materials hold great promise for photonics since they lead to ultracompact and efficient devices. However, their light compression is limited by fundamental constraints such as diffraction limit. To solve this problem, we employ highly anisotropic materials because anisotropy yields additional degree of freedom. It allows us to engineer structures with light compression beyond diffraction limit based on giant anisotropy in transition metal dichalcogenides. Therefore, our findings provide a building block for next-generation anisotropic nanophotonics.

Two-dimensional transition metal dichalcogenides possess two sets of optically addressable helicity-selective valleys (K+/K−) and provide a very promising material platform for the development of valleytronic devices [1]. In particular, van der Waals heterobilayers based on 2D transition metal dichalcogenides have been recently shown to support robust and long-lived valley polarization [2]. However, the roles of the chemical composition and geometric alignment of the constituent layers in the underlying dynamics remain largely unexplored. Here we study spin–valley relaxation dynamics in heterobilayers with different structures and optical properties engineered via the use of alloyed monolayer semiconductors [3]. Through a combination of time-resolved Kerr rotation spectroscopic measurements and theoretical modeling for Mo1−xWxSe2/WSe2 samples with different chemical compositions and stacking angles, we uncover the contributions of the interlayer exciton recombination and charge carrier spin depolarization to the overall valley dynamics. We show that the corresponding decay rates can be tuned in a wide range in transitions from a misaligned to an aligned structure, and from a hetero- to a homo-bilayer. Our results provide insights into the microscopic spin–valley polarization mechanisms in van der Waals heterostructures for the development of future 2D valleytronic devices. [1] J. R. Schaibley et al., “Valleytronics in 2D materials”, Nat. Rev. Mater. 1, 16055 (2016). [2] J. Kim et al., “Observation of ultralong valley lifetime in WSe2/MoS2 heterostructures”, Sci. Adv. 3, e1700518 (2017). [3] V. Kravtsov et al., “Spin-valley dynamics in alloy-based transition metal dichalcogenide heterobilayers”, 2D Mater. 8, 025011 (2021).

Strong light-matter interactions enable unique nonlinear and quantum phenomena at moderate light intensities. Within the last years, polaritonic metasurfaces emerged as a viable candidate for realization of such regimes. In particular, planar photonic structures integrated with 2D excitonic materials, such as transition metal dichalcogenides (TMD), can support exciton polaritons – half-light half-matter quasiparticles. Here, we explore topological exciton polaritons which are formed in a suitably engineered all-dielectric topological photonic metasurface coupled to TMD monolayers. We experimentally demonstrate the transition of topological charge from photonic to polaritonic bands with the onset of strong coupling regime and confirm the presence of one-way spin-polarized edge topological polaritons. The proposed system constitutes a promising platform for photonic/solid-state interfaces for valleytronics and spintronics.

We experimentally study quantum correlations in two-photon quantum walks at the edges of Su-Schrieffer-Heeger waveguide lattices. In these systems, topological protection serves to systematically enhance the broadening of the state compared to the trivial edge.

The feasibility of engineering quantum Hamiltonians with photonic tools, combined with the availability of entangled photons, raises the intriguing possibility of employing topologically protected entangled states in quantum optical computing and information processing. In this contribution, we describe physical mechanisms which contribute to the vulnerability of entangled two-photon states in topological photonic lattices and present clear guidelines for maximizing entanglement without sacrificing topological protection.

Recent experimental advances allow one to engineer topological models in bosonic systems like photonic crystals, coupled microwave resonators, or optical lattices experiments, among other platforms [1]. In parallel, experimental progress is also being made to couple quantum emitters to such platforms in order to obtain (or simulate) light-matter Hamiltonians [2-4] with topological photons. The emergent behaviour and applications of such topological quantum optics models, however, remain mostly unexplored. In this talk, I will discuss the emergence of unconventional quantum dynamics and interactions when quantum emitters are coupled to topological 1D waveguides [5] and 3D photonic Weyl environments [6]. We will show how the photon-mediated interactions induced by these topological photons give rise to the emergence of spin models with exotic and tunable long-range interactions, that can be used for quantum simulation purposes. References [1] Rev. Mod. Phys. 91, 015006 (2019) [2] Nature 508, 241–244 (2014), Nature Communications 5, 3808 (2014), Rev. Mod. Phys. 87, 347 (2015), Science 359, 666 (Feb 2018) [3] Nature Physics 13 (1), 48-52 (2017), Nature Communications, 9, 3706 (2018) [4] Nature 559, 589–592 (2018) [5] Science Advances 5, eaaw0297 (2019) [6] Phys. Rev. Lett. 125, 163602 (2020)

Recent works indicate that the propagation of quantum states can be protected by exploiting topology waveguide arrays. More recently, it has been suggested that topologically protected guided modes may also play an important role in the generation of photon pairs via parametric fluorescence, with quantum correlations of the generated photons in these systems being robust with respect to disorder that preserves the structure topology. In this talk we investigate the role of topological protection in waveguide arrays when pairs are generated via parametric fluorescence, either spontaneous four-wave mixing (SFWM) or spontaneous parametric down conversion (SPDC). We study the state robustness against positional disorder of the waveguides, characterized using the Schmidt number, fidelity, and density matrix. First, we consider the generation of nearly uncorrelated photon pairs in a silicon waveguide array and show that path quantum correlations are, in general, less robust than the linear properties of the system. Second, we focus on SPDC in a lithium-niobate waveguide array supporting two strongly coupled topological guided modes. We show that in this system it is possible to generate a hyper-entangled quantum state and that quantum correlations are, in general, robust due to topological protection. Finally, by comparing these two cases, we draw some considerations about the role photonic topological protection in the generation of photon pairs by third- and second-order nonlinear interactions.

Nowadays topological quantum states provide a new avenue in quantum technologies due to their robustness against disorder. While qubit arrays have recently become a popular experimental platform for testing topological effects in the quantum regime, experimental measurement of topological invariants for the entangled many-body states remains quite challenging. In this work, we generalize a method of the direct extraction of the topological invariant from the temporal dynamics of the two-photon mean chiral displacement. We consider a one-dimensional qubit array with dissipation and decoherence that corresponds to the interacting Su-Schrieffer-Heeger model in the two-photon sector. Tuning the wave function of the initial state, we determine the topological phase for the different types of states supported by the model that provides the two-photon extension of the bulk-boundary correspondence. Investigating the two-photon bound states, we demonstrate the topological protection of the doublon edge state that persists even in the situation when one of the bulk bands of the bound photons collapses.

We investigate analytically and numerically dynamics of dissipative Kerr solitons at the edge state of the Su-Schrieffer–Heeger model. We show that the one-dimensional edge state dynamics can be perturbed by the excitation of the bulk, which has two-dimensional nature. We discuss how this effect can be reduced in order to improve the soliton stability.

Optical resonances in nanoparticles enhance light-matter interactions and can therefore be utilized to greatly amplify light-induced forces. I will discuss some of our recent works on in this area, including 1) a comparison between of resonant plasmonic and high-index dielectric (Si) nanospheres for or optical tweezing; 2) manipulation of particles using plasmon-enhanced optothermal liquid flows; 3) construction of optically driven “metavehicles” that are able to propagate across a surface under plane wave illumination and be steered by the polarization of the incident light.

Optical modes engineering in metallic and dielectric nanoparticles could open new paths for assisting chemical transformations using sunlight. Photons, electrons, and phonons can be channeled and manipulated to create plasmonic and photonic chemical hotspots. Plasmons for example, have opened access to enhance and control chemical reactivity with CW illumination in the visible range, a fundamental requisite for sunlight photocatalysis. In recent years, we have investigated these phenomena at the single nanoparticle level in order to unravel the mechanisms inducing catalytic transformations at these illuminated interfaces [1-15]. Gaining a nanoscopic insight of these processes and their interplay could aid in the rational design of novel plasmonic and photonic photocatalysts. Further understanding and control of these processes could hopefully impact potential industrial applications of photocatalysis, which so far have remained elusive. 1. M. Barella, et al., ACS Nano 15, 2, 2458-67 (2021) 2. E. Cortes, et al., ACS Nano 14, 12, 16202–19 (2020) 3. J. B. Lee, et al, ACS Nano 14, 12, 17693–703 (2020) 4. S. Lee, et al., ACS Energy Letters 5, 12, 3881-90, (2020) 5. L. Hüttenhofer, et al., ACS Nano 14, 2, 2456-64, (2020) 6. J. Gargiulo, et al., Acc. Chem. Res. 52, 2525-35 (2019) 7. S. Lee, et al., Angew. Chem. 58, 15890-15894 (2019) 8. E. Pensa, et al., Nano Letters. 19, 1867-1874 (2019) 9. D. Glass, et al., Advanced Science 6, 22, 1901841 (2019) 10. S. Simoncelli, et al., Faraday Diss. 214, 73-87 (2019) 11. E. Cortés, Science, 362, 28-29 (2018) 12. R. Berte, at al., Phys. Rev. Lett. 121, 253902 (2018) 13. S. Simoncelli, et al., Nano Letters 18, 3400–3406 (2018) 14. S. Simoncelli et al., ACS Nano 12, 2184–2192 (2018) 15. E. Cortés, et al., Nature Comm. 8, 14880 (2017)

Here, we present a new implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media.

The refractory plasmonic materials are important for high temperature metamaterials in such applications as solar- or thermophotovoltaics. The spectral selectivity of metamaterials strongly depends on the losses of the plasmonic materials. Here we present an ellipsometric investigation of several thin films out of refractory plasmonic materials, such as W, Mo, Ir and TiN at temperatures up to 1000 °C. We show that the electron collision frequency grows linearly with temperature. Extrapolating the dependencies to temperatures above 1000 °C, we analyze the effects of this increase on the selectivity of metamaterial thermal emitters.

Photo-thermal therapy (PTT) is a rapidly developing approach for cancer treatment, that has greatly benefited from the tremendous advances in the synthesis of plasmonic nanoparticles (NPs), which can be used as light sensitive agents. This approach is based on the local induction of hyperthermia via light irradiation of plasmonic NPs in order to thermally kill cancerous cells. Such an approach ensures a high precision of treatment and the mechanism of action makes it as a valid alternative for treatment of malignant neoplasms with a multi-drug resistance. However, in order to minimize the adverse effects of PTT it is necessary to precisely measure and control the achieved temperatures at the tumor foci during light irradiation. Herein we report a novel technique to monitor intracellular temperatures during PTT based on temperature sensitive fluorescent dye, Rhodamine B. These findings may improve the quality of treatment and reduce unwanted adverse effects.

Application of different light-sensitive drug delivery carriers is limited due to a risk of overheating of living cells. Therefore, a real-time temperature monitoring within biological objects that controls the photothermal release of different cargos from light-sensitive carriers is highly demanded. In this work, we develop a multifunctional platform comprised of polymer microcapsules modified with nitrogen vacancies (NV) centers as nanothermometers and gold (Au) nanoparticles (NPs) as heating elements for the realization of laser-induced cargo release with a simultaneous temperature measurement inside cells. Such platform allows to prevent unwanted side effects related with the overheating of living cells and tissues.

The main objective of this talk is to present a new concept of remote data-monitoring with smart electronics labels without chip, and printed with regular printer. The core concept is the development of a reflectometry technique based on the use of resonant scatterers printed on a label. With these resonant scatterers, it is possible to extract Aspect-Independent physical quantities for identification or sensing purposes. Based on this idea, a novel versatile concept and method for wireless RF measurements / characterizations have been introduced. The development of this specific kind of reflectometry technique is midway between RF cavity and a quasi-optical free-space approach. In this paradigm, the tag composed of resonant scatterers is seen as a radar target where micro meter variations of its long or of its position can be monitored remotely. With such accuracy, it is possible to measure the temperature variation due to the physical elongation of the scatterer, or the humidity variation or even these two-physical quantities at the same time. It is also possible to detect displacements of the scatterers or its orientation relating to the reader antennas. The focused applications are in the field of identification and tracking. This technology can be seen as a new tool needed for the timely monitoring of goods. It could be seen as a sort of RF barcodes with extended functionalities compared to classical optical barcodes.

Parametric retrieval of electromagnetic properties is important for both new materials characterization and an accurate design of devices. While quite a few techniques have been developed over the years, precise mapping of high-permittivity samples remain challenging. Here we advance a so-called micro-strip technique, where transmission coefficients of a waveguide system with an analyte on top are used to extract electromagnetic parameters of the later. Our cross-like strip line configuration has a split ring resonator on one edge and an open circuit termination on another. This design allows performing a simultaneous test of cylindrical and rectangular samples. Our new post-processing scheme was tested on a water-filled container and showed 96.3% accuracy, assessed by comparing our results with tabulated data.

Radio frequency identification (RFID) is a widely used technology for contactless data readout. Numerous passive RFID tags are available on the market, and in a vast majority of cases, their designs are based on flat meandered dipole architectures. However, besides technological advantages, those realizations suffer from polarization mismatch issues and limited spatial sectors, from which flat tags can be interrogated. Here, we demonstrate and analyze a miniature omnidirectional tag accessible from all 4π stereo angles with a commercial RFID reader.

Radio frequency identification (RFID) allows to perform a wireless communication with special tags, attached to the objects. A lot of different tag’s antennas design have been explored. However, those realizations usually suffer from polarization mismatch issues, which leads to reading problems. Here we develop a new concept of miniature high-permittivity ceramic tags, stable to rotations in space. Due to a special holder, the tag takes a predetermined position in space, being insensitive to rotations. Our architecture has a compact size among typical RFID passive tags. Miniature RFID tags with stable reading, can find use in numerous applications.

Optomechanical systems in the quantum regime allow us to probe quantum mechanics at the boundary between the microscopic and macroscopic; these systems are also promising candidates for precision sensors of force and acceleration. By levitating an optomechanical system, that is, by suspending it in vacuum using optical or electromagnetic forces, we decouple it from its environment, a significant advantage for quantum applications. I will present recent results on feedback cooling and efficient position detection of a dielectric nanoparticle levitated in an ion trap. Furthermore, I will discuss the role that an atomic ion can play in enabling the preparation of nonclassical motional states of a nanoparticle, and will describe ongoing work to confine both a nanoparticle and an atomic ion under ultra-high vacuum.

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Laser cooling and trapping of neutral atoms and ions have led to advances in quantum information, quantum sensorics and fundamental physics. Applied techniques is limited by the continuous wave lasers mostly. This limits the class of atoms for laser cooling, trapping and manipulation. A lack of ultraviolet narrow-band lasers precludes laser cooling and trapping such atoms as hydrogen, antihydrogen, carbon, oxygen and nitrogen. It’s possible to use pulsed lasers (specially femtosecond lasers) to generate radiation in ultraviolet range of spectrum. In such a way the cooling and trapping of atoms realized under the pulsed interaction of atoms with laser field. We have demonstrated, for the first time, atom optical dipole trap using femtosecond laser radiation with pulse duration up to 70 fs. Atom’s lifetime in such trap is limited by the momentum diffusion due to dipole force fluctuations under high peak intensities of trapping field. Changing of temporal properties of atom-field interaction leads to the changing of spectral properties of trapped atoms. Experimental data show that at low intensities of localizing field the spectral properties of atoms are the same under the pulse and cw trapping: absorption line is shifted by the trapping field due to the ac-Stark effect. However, theoretical estimates show that increasing of pulsed intensity leads to the splitting of absorption line and under a “proper” intensity the spectral shift is absent. Such properties of pulsed optical dipole trap give the possibility for zero ac-Stark shift spectroscopy without the using trapping laser at a "magic" wavelength.

Natural materials typically interact weakly with the magnetic component of light which greatly limits their applications. This has led to the development of artificial metamaterials and metasurfaces. By utilizing strong optical resonant interactions in arrays of atoms with electric dipole transitions, we show how to synthesize collective optical responses that correspond to those formed by arrays of magnetic dipoles and other multipoles. Optically active magnetism with the strength comparable with that of electric dipole transitions is achieved in collective excitation eigenmodes of the array. By controlling the atomic level shifts, an array of spectrally overlapping, crossed electric and magnetic dipoles can be excited, providing a physical realization of a nearly reflectionless quantum Huygens’ surface with the full 2π phase control of the transmitted light that allows for extreme wavefront engineering even at a single photon level.

We investigate the spin dynamics and quantum thermalization of a macroscopic ensemble of S = 3 spins initially prepared in a pure coherent spin state. The experiment uses a unit-filled array of 10 thousand chromium atoms in a three dimensional optical lattice. Atoms interact at long distance under the effect of magnetic dipole-dipole interactions, realizing the spin-3 XXZ Heisenberg model. We investigated the buildup of quantum correlations during the dynamics, by measuring collective properties (total population in the seven different Zeeman states, collective spin length) and by characterizing spin fluctuations.

We consider a two-dimensional extension of the one-dimensional waveguide quantum electrodynamics and investigate the nature of linear excitations in two-dimensional arrays of qubits (particularly, semiconductor quantum dots) coupled to networks of chiral waveguides. We show that the combined effects of chirality and long-range photon mediated qubit-qubit interactions lead to the emergence of the two-dimensional flat bands in the polaritonic spectrum, corresponding to slow strongly correlated light.

Direct laser writing fabrication of metasurfaces allows for the unique opportunity of utilizing the height degree of freedom. This enables control over both geometric and propagation phase, and hence the full complex amplitude of manipulated wave fronts. We will present two applications: complex-amplitude orbital angular momentum holography, and optical trapping as well as achromatic imaging in fiber optics.

Here, we propose to marriage the laser-induced ultrafast magnetism and nanophotonics that together are able to efficiently excite and control spin dynamics in magnetic dielectric structures. In particular, we demonstrate that nanopatterning of a transparent magnetic dielectric film by a 1D grating of trenches allows to localize light in spots of tens nanometer size and thus launch the exchange standing spin waves of different orders. Relative amplitude of the exchange and magnetostatic spin waves can be adjusted on demand by modifying laser pulse polarization, incidence angle and wavelength. Nanostructuring of the magnetic media provides a unique possibility for the selective spin manipulation, a key issue for further progress of magnonics, spintronics and quantum technologies.

The chiro-optical effects complemented with polarization conservation and wavefront shaping finds potential applications in advanced imaging, sorting and detection of enantiomers and quantum optics. Here, a unique design strategy proposed to manifest enormous chiro-optical effects using achiral structures (instead of conventional chiral antennas). The basic building block of the meta-platform contains a pair of achiral structures. The underlying mechanism behind the giant chiro-optical effects is explained by numerically calculating the multipolar resonances of scattering power. The designed diatomic meta-platform achieves absolute control over spin and wavefront of incident light to demonstrate the polarization-conserved and -encrypted meta-holograms.

The ability to confine light at the nanoscale is one of the important goals for researchers in the path of developing integrated photonics and fully optical computers. The earlier approach for this is light localization in metallic waveguides by surface plasmons which utilizes metallic electrons oscillations coupling to the propagating electromagnetic surface waves. The approach is limited by high metallic absorptions and short path lengths. Naturally, broadband light cannot be localized with the same efficiency of charge carriers in conventional electronics with confinement lengths of few nanometers. This is an intrinsic feature of light behavior in bulk material - the optical path length of the light inside the material is directly proportional to the refractive index of the material. Thus, we need to overcome the limitation of physical material and develop materials with high refractive index contrast capable of strong light localization and guiding. In this work, we propose an inverse design framework based on conformal mapping. We demonstrate that it is possible to conformally map a virtual domain of arbitrary refractive index distribution to a physical domain of deformed reflective substrate. When illuminated this geometrical deformation emulates the propagation of light in high (or low) refractive index material. Designs of fundamental optical nanocomponets including nanoresonators of significantly high and low nondispersive refractive index are presented (fig.1). Finally, we show that the acquired high-index nanoresonator possesses high-Q quasi-BIC states which can be utilized for light trapping and channeling making subwavelength optical waveguide.

It has been shown recently that high-dimensional entanglement is a valuable resource for quantum communication. Besides, OAM-based qudits as a technique for encoding high-dimensional spatial states remains the only practical alternative for long-distance quantum communication in free space and in multimode fibers]. Thus, optical tomography of the light with OAM become an important task both for research and real applications. Although different techniques for OAM tomography exist at the moment, particularly with the use of spatial light modulators (SLMs), metasurface based methods can provide more practical alternative for tomography of quantum light. OAM sorters based on optical metasurfaces can be realized via the conformal coordinate transformation, which converts the helically phased light beam corresponding to OAM states into a beam with a transverse phase gradient, followed by a phase correction for the introduced distortion. In addition, conventional quantum state tomography methods employing SLMs require extra time and are subject to errors associated with the movement of bulk optical components or tuning of optical interference elements. In contrary, optical metasurfaces provide a noticeably stable and compact solution for projective measurements of quantum states being limited only by the used detectors. In this work we investigate a polarization insensitive silicon based metasurface for quantum tomography of photons with entangled orbital angular momentum. It is based on 2D arrays of silicon Mie-resonant nanodisks, in which both electric and magnetic dipole resonances can be excited in the near-infrared spectral range. Optimal parameters of the metasurface are numerically obtained by FDTD method using Ansys Lumerical software, while for the analysis of the optical wavefront shaping and consequent numerical demonstration of the classical OAM beam spatial sorting Zemax OpticStudio is used. Experimental samples of the metasurfaces are fabricated by consequent methods of electron beam lithography and reactive ion etching. For the base material we use hydrogenated amorphous silicon deposited on the glass by plasma enhanced chemical vapor deposition. Experimental characterization of the fabricated samples is performed using a custom table-top setup with SPDC source of entangled photons. Obtained results can be used for new functional and compact meta-devices for on-chip tomography of quantum light with OAM.

We report here on the first demonstration of the spin-orbit coupling between photons and phonons. We show that the spin angular momentum of phonons can be transformed into the orbital angular momentum of photons and vice versa during the fiber acousto-optic interaction. It results in acoustic - spin - dependent dynamically tunable generation of topologically charged optical vortex beams directly from a Gauss-like mode. This particular example of a ”two - field spin - orbit - interaction shows that the concept of the spin-orbit coupling can be generalized to the description of interaction between elementary excitations of different physical nature.

Topological materials in two dimensions (2D) are known to exhibit unidirectional, or chiral, edge states at the edges of the bulk. Such states must propagate along the edges of the bulk either clockwise or counterclockwise, and thus produce oppositely propagating edge states along the two parallel edges of a strip sample. Nevertheless, it is possible to construct the situation where edge states at the two parallel strip edges can propagate in the same direction; these anomalous topological edge states are named as antichiral edge states. The challenge to realize antichiral edge states stems from their underlying mechanism that can be described by a modified Haldane model. In the original Haldane model, the next-nearest-neighbor coupling picks a nonzero phase that accounts for the magnetic flux at the center of a unit cell. However, in the modified Haldane model, the next-nearest-neighbor couplings for different sublattices have opposite signs in phase, meaning that the two sublattices of A and B sites shall “feel” opposite magnetic fluxes. Here we demonstrate these antichiral edge states in a gyromagnetic photonic crystal. The crystal consists of gyromagnetic cylinders in a honeycomb lattice, with the two triangular sublattices magnetically biased in opposite directions. With microwave measurement, unique properties of antichiral edge states have been observed directly, which include tilted dispersion, chiral-like robust propagation in samples with certain shapes, and scattering into backward bulk states at certain terminations. These results extend and supplement the current understanding of chiral edge states.

Topological lattice defects are elementary lattice imperfections that cannot be removed by local changes to the lattice morphology, due to their topological character. Most classical wave topological metamaterials studied to date have been based on crystalline (defect-free) lattices, but introducing topological lattice defects into these lattices can have interesting effects. For example, adding a disclination to a valley photonic crystal can give rise to topologically protected freeform waveguide modes, which are much more robust against backscattering than those found in similar but topologically trivial amorphous lattices. In a separate demonstration, a three dimensional acoustic lattice containing an axial defect is shown to host robust vortex waveguide modes, which carry orbital angular momentum locked to the direction of propagation. These waveguide modes can be interpreted as a new type of Fermi arc generated by a strongly localized pseudo-magnetic flux associated with the topological lattice defect. Since, unlike real materials, classical metamaterials can be readily designed to incorporate topological lattice defects, there is considerable scope for exploiting the interplay between band topology (in momentum space) and topological lattice defects (in real space) in such systems.

For many years, the research focuses in topological photonics are on or related to the edge states. With the emergence of higher-order topological insulators, it became aware that in many topological phases of light, particularly for systems with vanishing Chern numbers, the edge states are not as robust as supposed. In this background, new fundamental topological properties are anticipated in place of the conventional bulk-edge correspondence. Here, we introduce two types of unprecedented fundamental topological responses: the bulk-disclination and bulk-dislocation responses. We show that these fundamental, quantized topological responses can serve as distinctive probes for various topological phases that share similar spectral features in both the edge and corner. We further show that these responses can lead to potential applications in trapping light into fully localized states for photonic applications.

We analyze light propagation in strongly coupled waveguide arrays, where the coupling between different waveguides is sufficient to shift some of the collective array supermodes above the light line, making them subject to radiative losses. Quasi-normal or leaky mode expansions provide an efficient formalism describing the propagation dynamics in this class of photonic lattices. Tuning the cutoff between bound and leaky modes provides a simple mechanism to controllably fill selected bands of the lattice. Using the leaky Su-Schrieffer-Heeger and Haldane models as examples, we propose a scheme to directly measure bulk topological invariants including the Chern number using radiative losses. Our approach is applicable to other non-interacting bosonic wave systems such as acoustics and exciton-polariton condensates, where the phenomena we have explored may be further enriched by effects such as spin-orbit coupling and inter-particle interactions. Reference D. Leykam and D. A. Smirnova, Probing bulk topological invariants using leaky photonic lattices, Nat. Phys. (2021). https://doi.org/10.1038/s41567-020-01144-5

The adoption of topological concepts in photonics uncovered unique opportunities in light control by means of topological edge states arising at the boundary of two photonic systems with different band topologies and enabling back-scattering immune light transport. Besides that, topological states may also revolutionize cavity-based electromagnetic devices such as lasers. A growing attention in photonic topological states engineering is drawn by time-reversal-invariant systems, which exploit lattice geometry adjustment to enable non-trivial band topology. However, the tether to geometry restricts topological edge states performance as well as their tunability. In the present work we put forward a new concept of the electromagnetic topological states engineering via alternating patterns of the particles' on-site properties rather than distances. That is, by introducing an additional degree of freedom related to sophistication of an individual scatterer (e.g., breaking its spatial inversion symmetry) we reduce the orchestration of topological properties to a single particle optimization. In electromagnetism, the inversion symmetry breaking leads to bianisotropy, or magneto-electric coupling, when external magnetic field induces not only magnetic but also electric dipole moment (and vice versa). The most interesting feature of bianisotropic particles in the context of our study is that the effective coupling between two particles depends on their mutual orientation, which can be quantified by the angle of their rotation. To get some insight into the coupling dependence on angle, we apply dipole model and seek for the eigenfrequency splitting near the lower-frequency hybrid dipole resonance. It is noteworthy that accounting for magneto-electric Green's dyadics, denoting the first correction to the quasistatic appoximation, is crucial to observe the splitting dependence on the angle of particle rotation. The obtained analytical results comply with full-wave numerical simulations. As a specific platform for the topological states realization we consider a two-dimensional array possessing C3 point symmetry of the lattice (kagome lattice). To demonstrate the universal nature of the studied physics we utilize both plasmonic (split-ring resonators) and all-dielectric (ceramic disks) platforms. Exploiting generic tight-binding model, we predict the existence of topological corner states protected by C3 symmetry and demonstrate them numerically . To sum up, we elaborated a novel recipe of photonic topological states engineering via alternating patterns of bianisotropic response. Contrary to the traditional symmetry protected topological systems, the proposed one enables unprecedented flexibility in edge states localization control and switching.

Anomalous Goos-Hanchen and Imbert-Fedorov shifts at anisotropic waveplate under near-normal incidence M. Mazanov1, O. Yermakov1,2, A. Bogdanov2, A. Lavrinenko3 1 V.N. Karazin Kharkiv National University, Kharkiv, Ukraine 2 Department of Physics and Engineering, ITMO University, St. Petersburg, Russia 3 Department of Photonics Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark The reflection and refraction of a plane electromagnetic wave are described completely by the Snell law and Fresnel amplitudes. However, for the electromagnetic beam of finite width, small polarization-dependent corrections to these laws emerge, namely, the spatial and angular longitudinal (Goos-Hanchen) and transverse (Imbert-Fedorov) shifts [1]. In essence, these shifts arise from the interference of plane waves constituting the beam, which have slightly different wavevectors and, hence, slightly different Fresnel amplitudes. The linear and angular shifts at not near-normal incidence are typically of the order of the light wavelength and the beam angular spectrum variance, respectively. However, in several specific regimes, such as near-Brewster incidence, material resonances, and weak measurements technique, the shifts can be anomalously large: linear of the order of beam width, and angular of the order of beam divergence. These regimes may be described in the anomalous weak measurements paradigm, in which the weak value (shift) may be enhanced in exchange for the reduction of output state norm (beam intensity). We report that anomalously large shifts of all four kinds could be obtained simultaneously at near-normal incidence, both in transmitted and reflected light, for a uniaxial plate with optical axis parallel to the interface (see also the figure in the full abstract file with problem geometry and schematics of the shifts). Similar to anomalous weak shifts, the new shifts depend on beam waist and beam divergence and are accompanied by beam profile deformations, while, in contrast to anomalous weak shifts, the output beam intensity is not dramatically reduced. The near-normal incidence singularity for the spacial and angular Imbert-Fedorov shifts was anticipated in approximate theory [1], however, to the best of our knowledge, this singularity has never been resolved explicitly. For the Goos-Hanchen shifts, the approximate expressions give no near-normal incidence singularity, while we find that near-normal GH shifts manifest a novel higher-order resonant singularity. We also note that anomalous IF near-normal shifts are closely related to the recently reported anomalous SHEL in a uniaxial crystal with optical axis perpendicular to the interface [2]. [1] K. Y. Bliokh and A. Aiello, J. Opt. 15, 014001 (2013). [2] W. Zhu, H. Zheng, Y. Zhong, J. Yu, and Z. Chen, Phys. Rev. Lett. 126, 083901 (2021).

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We prepare twist-controlled resonant tunneling transistors introducing small crystal lattice misalignment to monolayer (Gr) and Bernal bilayer (BGr) graphene electrodes graded by the crystallographic orientation. In such devices, we observe a series of bias and gate tunable conductive channels flowing through a thin layer of hexagonal boron nitride (hBN) forming the tunnel barrier. These channels emerge due to resonant tunneling transitions prompted by electric field-induced momentum displacement compensation. Our findings demonstrate explicit on-set and negative differential conductance (NDC) region resonances generated by the tunneling electrons that conserve principal laws. Moreover, our magnetotunneling results provide further confirmation of the tunneling mechanism inferred, revealing signatures of continuous transitions of chiral electrons.

We demonstrate the excitation of gate-tunable terahertz plasmon resonance in large area grating-coupled CVD graphene using Fourier spectroscopy. We find that the resonance is clearly distinguishable above the Drude absorption background in the 5-10 THz range despite moderate carrier mobility in CVD graphene (~10^3 cm2/V/s). Besides, plasmon lifetime in CVD graphene samples exceeds the transport relaxation from dc mobility measurements. We confirm this ratio by simultaneous THz transmission spectroscopy and field-effect measurements. We also show the plasmon spectra modification related to the presence of the grating coupler in close proximity to graphene. The plasmon field becomes tightly bound below the metal stripes, while the frequency depends on the stripe length but not by grating period.

Field-effect transistors with channels based on two-dimensional electronic systems (DES) are promising detectors of terahertz (THz) radiation. The sensitivity of such detectors can be significantly enhanced under conditions of plasmon resonance in a two-dimensional system. We consider a transistor THz radiation detector in the Corbino geometry, when a DES is connected to extended cylindrical contacts of the source and drain, and the photo signal from the THz antenna is applied between the source and the gate. This detector configuration can provide better response than the standard Dyakonov-Shura configuration. Indeed, as the radius of the internal contact decreases, the potential near it tends to the potential of an infinite charged filament, i.e. diverges logarithmically. Thus, a high field strength near the source leads to an increase in nonlinear effects. As such effects, we considered the hydrodynamic rectification of an alternating signal from a THz antenna.

The lens as a tool for focusing transmitted light has been around for many years. Conventional lenses have a geometric shape, i.e. they are optically thick, and rely on their geometry to imprint a proper phase shift onto a light wavefront making the wavefront converging by means of the difference in refractive indices. The lack of transparent materials with a high contrast of refraction indices limits this approach. The concept of planar or flat optics which has been expanding for the past decade consists in imprinting abrupt, controlled phase shifts onto transmitted light by a 2D array of subwavelength-thin nanoresonators, a metasurface. Thus, planar optical components can be made nanometre thin. Our eyes constantly dynamically adjust the focal length to keep the image in focus on the retina. Similarly, one of the desired functionalities of lenses is the active ultrafast and wide tenability which is still challenging. In the work, we put forward an original concept of a tunable Optical Magnetic Lens (OML) that focuses photon beams using a subwavelength-thin layer of a magneto-optical material in a non-uniform magnetic field. Tunability of the focal length of OML relies on changing the strength or curvature of the magnetic field. We applied the OML concept to a wide range of materials and found out that the effect of OML is present in a broad frequency range from microwaves to visible light. For terahertz light, OML can allow 50% relative tunability of the focal length on the picosecond time scale, which is of practical interest for ultrafast shaping of electron beams in microscopy. The OML based on magneto-optical natural bulk and 2D materials may find broad use in technologies such as 3D optical microscopy and acceleration of charged particle beams by THz beams. Moreover, using other magnetic field profiles, our OML can be reconfigured to operate as another optical component.

The Floquet theory for electrons in carbon nanotubes (CNTs) irradiated by a circularly polarized electromagnetic wave propagating along the CNT axis is developed. It is demonstrated, particularly, that the irradiation opens the gap between the conduction and valence bands of CNTs of metal type and lifts the degeneracy of electron states with mutually opposite angular momenta along the CNT axis. As a consequence, the optically-induced metal-insulator transition and the optical Zeeman effect appear in the CNTs. It follows from the theory that these light-induced phenomena can be observed in the modern experiments.

A suitable abstract will be generated soon.

Nuclear Magnetic Resonance Imaging (MRI) enables non-invasive imaging and localized spectroscopy of biological specimens extending from clinical applications to plant and environmental science applications. However, one of the main limitations of Nuclear Magnetic Resonance (NMR)-based techniques is their low sensitivity. Increasing the main magnetic field strength and optimizing the detector hardware are two strategies to overcome this sensitivity limit. We benchmarked the Signal-to-Noise Ratio (SNR) increase across different high-field systems. Furthermore, we tested the potential for implementing home-built radiofrequency (RF) coils for NMR-imaging at the state-of-the-art magnetic field strength of 22.3 T (f(1H) 950 MHz, uNMR-NL spectrometer). The SNR increase by a factor of 5.9 from 14.1 T to 22.3 T using similar 5 mm RF coils shows the potential for high spatial resolutions in MRI, faster total acquisition times and localized spectroscopy of low-concentrated compounds. Using a home-built 1.5 mm RF coil, the SNR increases by a factor of 3.5 compared to the 5 mm RF coil, and high spatial resolutions of (5.5 μm)3 can be achieved. We show the potential of using MRI at ultra-high field strength for investigating biofilms, sludge granules and plant roots. Opportunities comprise non-invasive metabolite detection in plant tissues by localized spectroscopy and high spatial and temporal resolutions. We identified susceptibility mismatches and resulting MRI image artefacts as one of the main challenges of imaging at ultra-high field strengths. Perspectives for ultra-high field MRI and localized spectroscopy, as well as possible solutions to encountered challenges, will be discussed.

T S Vergara Gomez1, 2, A Bakalli2, C Raynard1, M Dubois3, M Benamara3, D Bendahan1, F Kober1, S Enoch2, R Abdeddaim2 1 Aix Marseille Univ, CNRS, CRMBM, Marseille, France, 2 Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, France, 3Multiwave Imaging, Marseille, France A growing problem in magnetic resonance imaging (MRI) setups is the significant number of cables due to the use of complex multichannel radiofrequency (RF) coils in addition to the required sensors. Self-power sensors and coils driven by RF energy harvesting systems are a potential solution for this problem, as they would bring comfort to the patients and reduce the setup time. Previous studies performed on phantoms have demonstrated the possibility to harvest energy from the RF coils. However, the collected energy remains low. Therefore, we propose an alternative RF energy harvesting system based on high-efficiency rectifier diodes connected to a harvesting loop to maximize the energy recovered. Our system was design for a preclinical 4.7 T scanner to power a respiratory sensor during an in vivo experiment with minimal impact on the quality of the obtained images.

Radio-frequency (RF) harvesting is a promising technology for the wireless power supply of various in-bore devices used in magnetic resonance imaging. However, current technical solutions in this area are based on the conversion of linearly-polarized RF fields, and thus have some limitations. In the present work, we introduce and experimentally realize a novel harvesting setup allowing for the conversion of circularly-polarized RF field to direct current.

In this study the standardization method for T2* maps acquisition on various MR scanners (3T and 1.5T) is proposed. The reproducibility of the obtained T2* values is realized through the MR-compatible phantom containing paramagnetic complex iron oxide nanoparticles. The repeatability of measurements results has shown that the created phantom retains all the required characteristics (homogeneity, stability of concentrations and manifested paramagnetic properties) over a long period of time. The application of standardized T2* values allows to use previously received T2*, [ms] to iron concentrations in the dry substance of the liver (LIC), [mg/ml] conversion formulas for accurate, fast and non-invasive MRI diagnostics of liver iron overload.

T. Huber1, Ł. Dusanowski1, M. Moczała-Dusanowska1, M. De Gregorio1, J. Jurkat1, S. Klembt1, C. Schneider1, and S. Höfling1 1 Lehrstuhl für Technische Physik, Physikalisches Institut und Röntgen Center for Complex Material Systems, Am Hubland, 97070 Würzburg, Germany In 1997, Peter Shor presented an algorithm for prime factorization in polynomial time on a quantum computer1. Since the security in classical cryptography relies on the mathematical complexity of prime factorization, a possible realization of a quantum computer threatens classical cryptography. To fix this problem there are two possible solutions. One is post-quantum cryptography2 algorithms, which is still based on mathematical complexity. Here, the encryption is modified such that there is no known attack from a quantum computer. The other solution is quantum key distribution3, which is solely based on physical principles. The latter solution is preferable, because it is genuinely secure – also in the future. One concept to overcome the challenge of attenuation to establish long-distance quantum links is the quantum repeater4 which needs a local memory or a fully connected cluster state5, which probably needs a local qubit as well to build up the entanglement6. Spins in QDs are a promising platform, because their spins can be coherently controlled7, entangled with emitted photons8, or entangled with other distant spins9. We present our recent experimental developments on highly efficient, tunable self-assembled QDs in photonic structures toward functional quantum systems. References [1] P. Shor, SIAM J. Sci. Statist. Comput. 26,1484 (1997) [2] Daniel J. Bernstein: Introduction to post-quantum cryptography. Springer 2009 [3] C. Bennett and G. Brassard, Proceedings of IEEE International Conference on Computers, Systems and Signal Processing 175, 8 (1984) [4] H.-J. Briegel, W. Dür, J. I. Cirac, and P. Zoller, Phys. Rev. Lett. 81, 5932 (1998) [5] K. Azuma, K. Tamaki, and H.-K. Lo, Nature Comm. 6, 6787 (2015) [6] I. Schwartz et al., Science 354, 434 (2016) [7] D. Press D, T.D. Ladd, B. Zhang, Y. Yamamoto, Nature 456, 218 (2008) [8] K. De Greve et al., Nature 491, 421 (2012) [9] A. Delteil et al., Nature Physics 12, 218 (2016)

Admixing classical and quantum fields allows for easy yet powerful engineering of their quantum correlations [Laser Photon. Rev., 14:1900279, 2020]. Much of the Physics of coherently driven quantum optical systems follow this simple paradigm, where the nonlinear system typically produces squeezing, whose admixture with a fraction of the driving laser results in the observed output from the system, which is usually analyzed as a direct emission. Understanding the emission of the system in these terms allows tuning and/or optimizing its features, such as the amount of antibunching. We will focus as a particular case of this general theme on polariton blockade, and show the unifying and sui-generis features of the so-called conventional and unconventional types. In particular, we will show how bringing together both types of blockades takes the best of both worlds: robust, bright and strong antibunching from weakly nonlinear/highly dissipative systems, a configuration which remain to demonstrate experimentally.

Rydberg states of matter are in the focus of research nowadays due to their spectacular properties and prospects for applications in quantum technologies. Excitons -- bound electron-hole pairs in semiconductors -- are the analogues of hydrogenic atoms. Cuprous oxide crystals host series of excitons with the principal quantum number n limited by 25 … 28 whose spatial extensions reaches micron scales [1] offering versatile platform for realization of Rydberg physics. We theoretically study Rydberg excitons in one-dimensional lattices formed by the traps in Cu2O semiconductor. The triplet of optically active p-shell states acts as an effective spin 1, and the van der Waals interactions between the excitons are strongly spin dependent. We predict that the system has the topological Haldane phase with the diluted antiferromagnetic order, long-range string correlations, finite excitation gap, and, importantly, the edge states behaving akin to spin-1/2 fermions. Combining numerical diagonalization techniques, variational ansatz, and the infinite time evolving block decimation approach we address the properties of the ground state and elementary excitations in the system. We analyze the effect of the trap geometry and interactions anisotropy on the Rydberg exciton spin states and demonstrate a rich spin phase diagram of the system [2]. We also study the fine structure of the ground state in the finite chains resulting from the effective interaction of the edge spins. These edge states can be detected optically via the enhancement of the circular polarization of the edge emission as compared with the emission from the bulk. The distribution of the exciton angular momentum vs. trap number in the chain is calculated numerically and analytically [3]. [1] T. Kazimierczuk, D. Frohlich, S. Scheel, H. Stolz, and M. Bayer, Giant Rydberg excitons in the copper oxide Cu2O, Nature 514, 343 (2014). [2] A.N. Poddubny and M.M. Glazov, Topological spin phases of trapped Rydberg excitons in Cu2O, Phys. Rev. Lett. 123, 126801 (2019). [3] A.N. Poddubny and M.M. Glazov, Polarized edge state emission from topological spin phases of trapped Rydberg excitons in Cu2O, Phys. Rev. B 102, 125307 (2020).

Entangled photons are highly demanded for quantum optical applications, such as quantum communication, imaging and spectroscopy. One way to generate entangled photons is via spontaneous parametric down-conversion (SPDC), where a pump photon interacting with a second-order nonlinear material is down-converted into two daughter photons (biphotons) of lower frequency. Typically, SPDC utilizes millimeter scale nonlinear materials to achieve a relatively high conversion efficiency, compromising its scalability and integrability. ln an effort to achieve scalable SPDC sources, we demonstrated SPDC in subwavelength nonlinear films [1], albeit with a lower efficiency due to the ultra-small nonlinear interaction length. Biphoton from ultrathin SPDC sources are very attractive for quantum optical applications because of their high degree of spatial and frequency entanglement. Promising platforms for enhancing SPDC are subwavelength optical metasurfaces, where geometric resonances have been used to boost to nonlinear optical interactions. For example, for second harmonic generation (SHG) the conversion efficiency has been enhanced up to four orders of magnitude in Fano resonant metasurfaces. The generation of nonclassical states of light in resonant metasurfaces is actively investigated nowadays. Many theoretical works have suggested different metasurface designs aimed at enhancing the efficiency of SPDC at the subwavelength level. Unlike SHG, experimental observation of SPDC in metasurfaces still remains a challenge. Meanwhile, SPDC with a moderate rate has been observed in a dielectric nanoantenna supporting Mie-like resonances [2]. Very recently, we achieved biphotons generation via SPDC driven by Mie-like resonances in subwavelength metasurfaces made of LiNbO3 [3]. Such metasurfaces were already used to boost SHG [4]. By generating biphotons near the electric-dipole resonance of the metasurface, we demonstrated a 130-fold enhancement of the biphoton generation rate, compared to an unpatterned film of the same thickness and material. Moreover, by tuning the resonant wavelength, we show how metasurfaces can be used to engineer the frequency spectrum of the emitted biphotons, leading to either narrowband or broadband biphotons. We envisage that metasurfaces supporting high-Q resonances such as Fano resonances or bound states in the continuum could be used to further enhance the conversion efficiency. Our results bridge the gap between nano-optics and nonlinear quantum optics. They establish ‘quantum’ optical metasurfaces as promising sources for the generation and engineering of complex biphoton states and pave the way to the development of multifunctional flat-optics platforms. Acknowledgements T. S. C. and M. A. W. are part of the Max Planck School of Photonics supported by BMBF, Max Planck Society and Fraunhofer Society. References [1] T. Santiago-Cruz et al., Entangled photons from subwavelength nonlinear films, Opt. Lett. 2021, 46, 653-656 [2] G. Marino et al., Spontaneous photon-pair generation from a dielectric nanoantenna, Optica 2019, 6, 1416–1422. [3] T. Santiago-Cruz, et al., Spontaneous Parametric Down-Conversion from Resonant Metasurfaces, arXiv preprint 2021, arXiv:2103.08524. [4] A. Fedotova et al., Second-Harmonic Generation in Resonant Nonlinear Metasurfaces Based on Lithium Niobate, Nano Letters 2020, 20 (12), 8608-8614.

We develop a microscopic theory of the quantum Zeno effect in a spin-photon interface represented by a charged quantum dot in a micropillar cavity in the strong coupling regime. With increase of the probe power, the spin precession frequency in an external magnetic field decreases and eventually vanishes due to the quantum Zeno effect. We calculate the spin noise bispectrum, which reveals the qualitative change of the spin statistics with an increase of the measurement strength. For the zero magnetic field we calculate the quantum information gain rate and find the conditions when it equals the spin dephasing rate, i.e., reaches the quantum limit for the nondemolition spin measurement.

We have investigated the influence of lattice sites vibrations on bosonic Hofstadter's butterfly (HB) spectrum for the case of conventional square lattice. Only the pair of specific phonon modes with opposite quasimomenta has been taken into account. The study has shown that HB-type spectra can be substantially modified by the presence of phonons, depending on the ratios of such parameters of the system as site-to-site transition amplitudes, particle-phonon interaction constant, and characteristic vibration frequency.

We suggest the concept of electromagnetic chirality based on a precise shaping of bound states in the continuum in asymmetric metasurfaces. The approach allows boosting the chirality up to its ultimate maximum for metasurfaces remaining transparent to waves of one circular polarization, but blocking resonantly waves of the opposite polarization. The latter are absorbed by rotationally symmetric metasurfaces or are reflected by metasurfaces with no point symmetries. We demonstrate the specific designs of optical metasurfaces based on silicon bars and also present proof-of-concept microwave experimental results.

Optical sensors can play vital roles in emerging applications such as augmented reality and autonomous driving. Conventional optical sensors, such as the smartphone camera, can only acquire light intensity in two dimensions. In order to further obtain the depth, polarization, and spectral information of the target object, it is often required to use bulky and expensive instruments. Metasurface is composed of an array of optical antennas that can manipulate the amplitude, phase, polarization, and spectrum of light at the subwavelength scale. By replacing conventional diffractive of refractive elements with metasurfaces in imaging systems, one may be able to build optical sensors for high-performance multidimensional light sensing with a low size, weight, and power. In this talk, I will present our recent progress towards this goal.

We design metasurfaces based on silicon films with smooth relief described by several Fourier harmonics and study their ability to redirect the refracted light over a wide angular range controlled by subtle variations of the optical setup. We use semi-analytical approach based on the Rayleigh hypothesis as well as full-scale numerical solutions to optimize the relief shape. To illustrate the reconfigurability potential, we design metasurfaces efficiently redirecting the refracted light from 83° to -73° with respect to the normal, when the angle of incidence is varied from 0° to 2°, and from 80° to -74°, when the substrate permittivity is altered from 2.3 to 2.2.

In recent years, dielectric metamaterials have become a fast-growing trend in modern electromagnetics. In particular, the double-negative response, i.e., simultaneously negative permittivity and permeability, of a dielectric metamaterial is of interest. To match both magnetic and electric responses at the same frequency, several methods have been proposed, such as metallic coatings for an additional plasmonic response, non-spherical particles, sub-lattices of particles of different sizes, dielectric-coated metal particles, and all-dielectric core-shell particles based on the exceptionally high values of the refractive index at microwave frequencies [1]. In this study, we propose [2] an all-dielectric meta-atom design for a double-negative metamaterial (DNM), which may provide low loss and high scalability. By using three-layer radially inhomogeneous dielectric spherical structures, one may achieve a simultaneous excitation of electric and magnetic dipole Mie resonances at up to visible light frequencies (see Fig. 1). As a result, an array of such particles at a sufficient concentration shall simultaneously have negative effective permittivity and negative permeability, i.e., shall behave as a DNM. Moreover, due to isotropy, an ensemble of the proposed meta-atoms does not need any special arrangement to provide a double-negative response. Thus, as a particular realization, such particles can be suspended in a fluid, forming a liquid DNM, which presents even more possibilities for controlling electromagnetic waves. The proposed structure was first optimized within the analytical approach to achieve the matching of the magnetic and electric dipole Mie resonances. Then, the double-negative response was confirmed by the simulations.

We study versatile soft-matter metasurfaces based on self-assembling of nematic liquid crystal on polymer alignment layers processed with a focused ion beam. Digital control of the beam path allows imprinting patterns that induce different complex distributions of the refractive index within several micrometer thick liquid crystal layers. We optimize them to implement various optical functionalities, such as broadband anomalous refraction, wide-aperture focusing, and beam splitting in tens of channels.

We consider a light trapping in a quasicrystal slab. We call a light trapping the effect when microwave radiation of a certain wavelength enters the quasicrystal slab and cannot leave it, while for other wavelengths the quasicrystal remains transparent. To obtain the medium with such properties, the reciprocal space engineering method is used. The effect is observed in the microwave region. The experimental results are in a good agreement with the theory and the numerical simulations.

In order to harness the intrinsic ability of colloidal semiconductor nanocrystals to couple strongly with light, it is important to efficiently outcouple energy from photoexcited quantum dots (QDs), much like how nature uses molecular antennas to direct light during photosynthesis. This talk focuses on aromatic acceptor ligands for triplet-fusion based photon upconversion, where orbital overlap between the QD donor and molecular acceptor is critical for efficient energy transduction. In the past 5 years, we have learnt a great deal about how the electronic interactions between chalcogenide nanocrystals and acene conjugated molecules affect the photon upconversion quantum yield. We apply the lessons learnt to extending photon upconversion to silicon nanocrystal light absorbers and thin films, addressing synthetic and self-assembly challenges with invaluable insight from time-resolved spectroscopy.

GaN/AlN monolayer-thin quantum wells represent a unique epitaxially grown semiconductor structure in which strong excitonic effects control optical properties up to room temperature, owing to extreme quantum confinement within a single GaN monolayer. I will introduce experimental studies of the picosecond emission kinetics in both single and multiple (up to 100) GaN/AlN quantum wells grown by molecular beam epitaxy, which allowed us to identify the dominant exciton relaxation process as a fast relaxation of dipole-allowed “bright” excitons, accompanied by a spin flip and transformation into spin-forbidden “dark” excitons, whose levels are split off by ~40 meV due to the electron-hole exchange interaction enhanced by the extreme 2D confinement. Despite the “dark” nature of the ground exciton state and the large value of the exchange splitting between dark and bright excitons, GaN/AlN ultra-thin quantum wells are remarkably effective UV light emitters at temperatures on the order of and above 300 K, which is determined by a sufficiently effective thermal filling of bright excitonic states under conditions of high efficiency of the exciton channel of radiative recombination and low efficiency of nonradiative recombination processes. This combination of properties makes these structures very promising for applications as an active region of UV light-emitting devices. As a confirmation, I will present electron-beam pumped emitters based on GaN/AlN multiple monolayers, operating at 300 K in the spectral range of 235-260 nm with a pulse power exceeding 1 W.

Self-organized InP/GaInP2 quantum dots (QDs) grown by metal-organic chemical vapor epitaxy on [001] GaAs represent natural Wigner and anyon molecules (WAMs) and are promising candidates for realization of topological quantum gates, as was demonstrated recently using high-spatial-resolution (HSR) photoluminescence (PL) spectroscopy. Due to a very strong PL intensity and efficient cavity-mode-QD coupling they provide the lowest lasing threshold of optical micro-resonators and are interesting for nano-photonic applications. In situ formation of WAMs in these QDs, i.e. electron doping and built-in magnetic field, emerges due to a spontaneous atomic ordering (AO) of GaInP2 and its correlation with a strained-layer epitaxy and QD self-assembly. This results in the formation of piezo-electric (PE) core-shell composites, in which the InP QDs are surrounded by AO domains (AODs) generating strong PE fields. Here we present our results on growth experiments, including selective area epitaxy, structural, optical and PE fields measurements for control and optimization of the properties of these composites for quantum computing and photonic applications.

Site-controlled growth of quantum dot objects has a high potential for both: device applications and fundamental studies. Development of site controlled growth technique is quite a bit challenging since it implies the need of a high quality of semiconductor material and pre-growth processing, which means that the growth surface contacts with chemicals. Our investigation have shown that most chemicals used for pre-treatment of the growth surface are reducing the intensity of InP quantum dot (QD) photoluminescence (PL) signal indicating on the quality degradation. QD’s have been grown by metal organic vapor phase epitaxy (MOVPE). The only combination that does not reduce the PL signal of QD’s was shown to be an e-beam evaporated SiO2 film developed with a diluted HF based etchant. Importance of stoichiometric composition of SiO2 film have been established and oxygen incorporation into the underlying semiconductor was shown to be the reason of degradation. We used e-beam lithography to create apertures for QD growth. However this appears to be not enough to step down to a single QD growth regime: the use of electron beam lithography is not the only key to obtain small apertures. Wet etching process is not as simple and it appears that we need to over-etch the SiO2 film to make sure that all the “scum” has been removed from the surface. As a result minimal size of the aperture exceeds 300 nm (500 nm normally) which is too much for a single QD. We have developed a two-step lift-off lithography process based on the combination of SiO2/SiNx films. The method is based on the difference of the etching rates of SiO2/SiNx combination and is shown to preserve the initial lithography dimensions. Low temperature photoluminescence signal of uncovered InP QD’s has been registered. The GaInP selective epitaxy regrowth process has been studied. It was shown that In to Ga ratio in the solid phase strongly depends on the aperture size which is explained by the difference in the horizontal transport of the atoms in the MOVPE growth.

In this report we show that despite the symmetry and lattice constant mismatch high optical quality GaP thin films can be grown on transparent sapphire wafers. Complex refractive index measurements by means of spectroscopic ellipsometry, confirmed that optical constants of the epitaxial layers are close to bulk GaP values. Fabrication of optically resonant GaP nanostructures on as grown structures using electron-beam lithography and inductively coupled plasma etch is demonstrated.

To date, nanoscale dielectric and plasmonic systems with a nonlinear response are of great interest to researchers. This is due to a wide range of their potential applications in nonlinear optical converters and optical communication systems. The fundamental problem of nanoscale frequency converters is the low efficiency of nonlinear optical generation. The reason for this is that the main mechanism for increasing the efficiency of nonlinear signal generation via phase matching is not available at scales smaller than the wavelength. Here, we experimentally investigate the generation of the second optical harmonic in hybrid GaP/Au nanoparticles resonantly enhanced with plasmonic and Mie resonances. Using dark-field spectroscopy, it is shown that nanoantennas support a series of optical resonances in the visible range, the spectral position of which is in good agreement with the numerical simulation. We measured the second harmonic generation spectrum, with sharp resonances which is in accordance with linear scattering. Finally, the dependence of the second harmonic optical signal on the polarization is measured.

We analyze the multipole collective effects in the nanostructures made of lossy, layered, and high-index materials. The periodic arrangement of nanoparticles into array results in the excitation of multipoles lattice resonances, and the latter can be controlled by the lattice period. Resonances in the nanoparticles made of transition metal dichalcogenides and other van der Waals materials can be substantially enhanced by the collective phenomena in the periodic array.

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Enhanced light-matter interaction in polar crystals attracts considerable attention since the latter support phonon polaritons (PPs) - hybrid electromagnetic modes involving atomic vibrations. PPs in the thin slab of van de Waals materials (vdW) demonstrate long lifetime and ultra-high field confinement which can lead to intriguing vibrational strong coupling (VSC) phenomena and potential sensing applications. Recently VSC between h-BN nano-resonators and molecular vibration has been demonstrated. However, the basic interaction between molecular vibrations and propagating PPs in unstructured slabs of the vdW materials has not yet studied. In this work, we use nanoimaging techniques to study the interaction between propagating h-BN PPs and organic molecular vibrations. We performed near-field polariton interferometry, showing that VSC leads to the formation of a hybrid mode with a pronounced anti-crossing region in its dispersion. Our work shows the fundamental study of the strong-coupling between molecular vibration and propagating PPs.

In this work we show how to excite ultra-confined anisotropic polaritons in vdW crystal slabs and at the same time preserve their properties by creating a periodic gold grating below the flake. We consider slabs of MoO3, which have recently been used in various near-field polaritonic experiments. By both experimental and theoretical analyses, we identify the excitation of hybrid high-order Fabry-Perot resonances. We demonstrate that the resonances strongly depend upon the angle between the main optical axes of the MoO3 slab and the Bragg vector of the metal grating. Moreover, our analysis enables us to reconstruct complex anisotropic isofrequency surfaces of polaritons, revealing different regimes (e.g. elliptical and hyperbolic)

Hyperbolic surface polaritons in the natural van der Waals (vdW) crystals or metamaterials, exhibiting in-plane hyperbolic dispersion, lead to ray-like propagation with large wavevectors and enhanced density of optical states along with certain directions of the material surface. These unique polaritons offer unprecedented possibilities for manipulating infrared light in a planar optical circuitry at the nanoscale. In this work, we, for the first time, theoretically predict and experimentally demonstrate the focusing of ray-like phonon polaritons (PhPs) on the surface of thin slabs of α-MoO3 with deep-subwavelength foci sizes of ~\lambda_0/50, being \lambda_0 the incident photon wavelength in free space. We do this by introducing metallic nanoantennas with convex geometries as novel optical elements in nano-optics for both launchings and focusing of ray-like polaritons. Remarkably, these foci exhibit enhanced near-field confinement and absorption compared to foci produced by PhPs exhibiting in-plane isotropic dispersion. Our findings pave the way towards developing (bio)sensing, infrared spectroscopy, or light-harvesting applications with enhanced performances at the nanoscale and compatible with on-chip planar technologies.

We developed the theory of resonant optomechanincal interaction between electromagnetic field and flexural vibrations of 2D materials. We predict that the mechanical properties of transition metal dichalcogenide monolayers can be controlled by optical excitation with the frequency close the exciton resonance. We also demonstrate that the presence of flexural vibrations enables efficient excitation of plasmons in graphene. Two-dimensional membranes demonstrate unique mechanical properties due the presence of flexural modes in their vibrational spectrum. In contrast to conventional acoustic vibrations, such modes have quadratic dispersion law which boosts nonlinearities leading to non-Hookean elasticity and crumpling phase transitions. Here, we present the theory of interaction between flexural vibrations and electromagnetic field in atomically-thin two-dimensional materials, such as graphene and transition metal dichalcogenides, which possess strong optical response governed by plasmon and exciton resonances. We show that illumination of a transition metal dichalcogenide monolayer by a plane electromagnetic wave, apart from well-known radiation pressure force, can also affect directly the layer tension. Such optomechanical tension is due to the coherent interaction between light and flexural vibrations of the layer [1]. The induced tension can be both positive and negative. When the excitation frequency is below the exciton resonance, the light stretches the layer. The induced tension depends to the incident light polarization and can be strongly anisotropic. If the excitation frequency is above the exciton resonance, the light tries to crumple the layer. Then, the optomechanical crumpling force competes with the bending rigidity of the layer and the radiation pressure force that try to flatten the layer. When the excitation intensity surpasses the critical value, which is inversely proportional to the temperature, the layer becomes instable with respect to buckling with the wave vectors in a certain range, leading to the phase transition to the crumpled state [2]. In graphene, flexural vibrations can facilitate excitation of plasmons. The plasmon can be generated by the normally incident light in the process of Stokes or anti-Stokes scattering with emission or absorption of a flexural phonon. We identify the mechanisms of the interaction between plasmons and flexural phonons that are dominant at low and high temperatures: the shift of the vibrating layer with respect to the electromagnetic field and the flexion-induced deformation potential, respectively. Using the developed microscopic theory, we calculate the temperature dependence of the flexural-phonon-assisted plasmon generation efficiency. [1] A.V. Poshakinskiy and A.N. Poddubny, Phys. Rev. X 9, 011008 (2019). [2] I.D. Avdeev, A.N. Poddubny, and A.V. Poshakinskiy, ACS Photonics 7, 2547 (2020).

Transmit array systems are designed for overcoming the field-inhomogeneity problems of ultra-high field systems. They can also be helpful for conventional MRI scanners. There are three major problems associated with birdcage-coil-based RF transmission systems in conventional scanners. First, the RF power is delivered to the whole body even when only a specific part of the body needs to be excited. Usually, MR scan time is elongated to reduce associated heating. The increased scan time not only causes an increase in cost but also degrades the image quality. Second, MR scanning in the presence of metallic implants or interventional devices may not be possible due to RF-induced currents on the long metallic structures. The radiologists are hesitant to scan patients with metallic implants. For the MR-guided interventions, special devices need to be developed. Third, high-power systems (15 to 20kW RF power is used in conventional MRI systems) have high maintenance and capital costs. This is one of the main factors in making MR scanners expensive. The use of transmit array systems can solve all of these three problems. In this talk, the transmit array system developed in our research center will be discussed.

The presentation will focus on most recently developed novel antenna array designs that enable imaging of human head and body at the currently highest available MR field strength of 10.5T. At the associated UHF operating frequency of 447 MHz significant challenges arise. The talk will include discussion and examples of how incorporation of high dielectric constant materials can aid antenna design, reduce SAR and enhance SNR.

Magnetic Resonance Spectroscopy of X-nucleus is a method for mappingmetabolite quantity in-vivo in the desired region of the human body. However, this methodhas a lot of difficulties. Since natural abundance of X-nucleus is much lower than for hydrogen,to improve SNR of the spectrum we need to work in higher static magnetic fields. But, even atsuch high fields, X-nuclei imaging still a very difficult process. One of the problems are RF-coils,which are required for transmission and reception of signals. Traditionally, for human body X-nuclei MRS multi tuned loop coils are used. However, such coils suffer from additional losses inthe circuits required for tuning double-frequency tuning and high complexity. In this work, wepropose an alternative approach, based on a recently introduced leaky-wave antenna for MRI,that allows creating wideband excitation which provides wideband transmit and receive. Thiswideband frequency range covering13C,23Na and31P Larmor resonant frequencies.

In this work, we investigate the optimal coefficients of the exponential current excited on a leaky wave surface coil. The respective functional is first derived analytically and later computed numerically using Python. The results are compared to the same problem modeled in Comsol Multiphysics.

In this work, we compare three types of transceive wireless coils: Helmholtz-type coil, metamaterial-inspired coil and their combination. Each transceive coil is electromagnetically coupled to a body coil "birdcage" type of a 1.5 T MR scanner and improves bilateral breast imaging performance. While Helmholtz-type coil and metamaterial-inspired coil based on coupled split loop resonators are linearly polarized, their combination allows to couple with both linear components of the radiofrequency magnetic field, providing a more significant effect of a local boosting of the body coil's transmit efficiency and radiofrequency safety in comparison with birdcage coil only.

I will present recent results from our group on stationary and non-stationary states of matter that are realised by quantum systems where light and matter are strongly coupled. These systems include atom-cavity setups as well as atomic ensembles which are interacting with the guided modes of a waveguide. They allow the investigation of a variety of phenomena including pattern-retrieval phase transitions in associative memories, the emergence of time crystal phases as well as the realisation of quantum engine cycles relying on time-translation symmetry breaking. [1] G. Buonaiuto, F. Carollo, B. Olmos and I. Lesanovsky, Dynamical phases and quantum correlations in an emitter-waveguide system with feedback, arXiv:2102.02719 (2021) [2] E. Fiorelli, M. Marcuzzi, P. Rotondo, F. Carollo and I. Lesanovsky, Signatures of associative memory behavior in a multi-mode Dicke model, Phys. Rev. Lett. 125, 070604 (2020) [3] F. Carollo, K. Brandner and I. Lesanovsky, Nonequilibrium many-body quantum engine driven by time-translation symmetry breaking, Phys. Rev. Lett. 125, 240602 (2020)

Photons are often considered to be nearly perfect carries for quantum and classical information processing. Yet, building gates with photons is a challenging task. One of the approaches to solve this problem is to utilize coupling of photons with commons spin system using high Q-factor and low mode volume cavities. As a spin system we aim to use diamond color centers which do have quite broad spectrum thus making it important to use cavities, operating in single-mode regime. Photonic crystal cavities satisfy this condition and have small mode volumes accompanied with high quality factors. In this report, we demonstrate nanobeam Si3N4 photonic crystal cavities with Q as large as 24000. The cavities were measured via tapered optical fibers, which were attached to on-chip devices. We demonstrate a coupling efficiency of 96%. This work is useful for quantum optics applications, including long-distance quantum networking and optical quantum computing.

see the attached file

In modern quantum optics chiral waveguide quantum-electrodynamical (wQED) systems are attracting a lot of attention from the perspective of fundamental science, and possible interesting applications. In our work we theoretically analyze the eigenstates in a two-excitation domain of an ensemble of two-level atoms that are periodically spaced, and asymmetrically coupled to a guided mode. We found that in a regime when all atoms emit photons in-phase, most eigenstates in such a system can be well-approximated and described through the eigenstates from a single excitation domain, while the rest present a superposition of bound states with two strongly attracting excitations, and states, for which the excitations strongly repel from each other occupying the opposite edges of the system.

Tailoring of the light-matter interaction at nanoscale attracted a lot of attention in the last decades due to increased technological capabilites of creating various optical nanostructures and their potential in the development of compact and scalable optical and quantum integrated components and circuits based on the deterministic nanophotonic interfaces between the quantum emitters (QE) and light. One of the recently proposed ways to achieve this goal is based on the so-called chiral light-matter interaction [1] that manifests itself in asymmetric interaction between the QEs with circularly polarized dipole transition moments and localized optical modes propagating in opposite directions. One of the most suitable technology that allows to realize such structures is based on a semiconductor platform that allows for integration of planar optical circuits with quantum dots during the growth process [2]. Up to now the most reliable way to efficiently control the emission properties of the quantum dots was the use of photonic crystal (PhC) waveguides and cavities with experimentally demonstrated asymmetry of coupling close to 100% [3,4]. However, in such systems both coupling asymmetry and strength are quite sensitive to the position of emitter due to the strongly inhomogeneous field of the PhC modes. Lately, an alternative to the PhC based systems in the form of various nanostructures composed of Mie resonant dielectric and semiconductor nanoparticles is being extensively explored [5]. Such bottom-up approach allows to design structures with different geometry and with different optical properties by careful tuning of their individual building blocks and coupling between them. In this work, we propose an approach for design of an optical nanostructure based on a periodic waveguide that can serve as an efficient chiral interface between the propagating waveguide modes and the circularly polarized dipole sources embedded in the structure. This approach relies on the two factors: presence of two quasi-degenerate orthogonal modes in a periodic waveguide, and specific type of the dispersion of the whole structure possessing a stationary inflection point. Combination of these factors allows to increase the strength of the light-matter interaction while at the same time keep the interaction highly asymmetric. Moreover, unlike other designs studied before, the coupling of a quantum source to the mode of the proposed structure is substantially more tolerant to the position of the source, which makes it beneficial from the practical point of view. We believe, that the presented results will enrich the variety of the designs of compact chiral nanophotonics interfaces for further development of efficient and scalable integrated quantum circuitry. The work was supported by the Russian Science Foundation, Grant No.19-72-10129. R.S. acknowledges the support by the Grant from the President of Russian Federation MK-4418.2021.1.2. References [1] Lodahl P, Mahmoodian S, Stobbe S, Rauschenbeutel A, Schneeweiss P, Volz J, Pichler H, and Zoller P. 2017 Nature 541 473. [2] Lodahl P 2018 Quantum Sci. Technol. 3 013001 [3] Söllner I, Mahmoodian S, Hansen S L, Midolo L, Javadi A, Kiršanskė G, Pregnolato T, El-Ella H, Lee E H, Song J D, Stobbe S, and Lodahl P 2015 Nature Nanotechnology 10 775 [4] Mehrabad M J, Foster A P, Dost R, Clarke E, Patil P K, Fox A M, Skolnick M S, and Wilson L R 2020 Optica 7 1690 [5] Kuznetsov A I, Miroshnichenko A E, Brongersma M L, Kivshar Yu S, and Luk’yanchuk B 2016 Science 354

We examine an array of atoms harmonically trapped in the vicinity of a chiral waveguide. We show that this optomechanical system directly maps to generalized quantum Rabi model and present connection between the self-organization of atomic chain and quantum phase transition in such structure. We extend the class of the superradiant phase transitions for the systems possessing $\mathbb{Z}_3$ rather than parity $\mathbb{Z}_2$ symmetry and demonstrate the emergence of the multicomponent Schrodinger cat ground states in these systems.

Dielectric periodically structured nanodevices play a key role in nonlinear optics due to their remarkable capability of boosting frequency conversion efficiency. This brings new perspectives in both fundamental research and practical applications in photonics, sensing, and quantum optics. In this context, we propose two double-resonant nonlinear optical nanostructures for enhancement of the second-harmonic generation (SHG): a cruciform silicon array covered by a monolayer MoS2 and a photonic crystal slab waveguide made of SiN. In both cases we demonstrate that by taking advantage of optical bound states in the continuum, one can engineer high-Q resonances characterized by strong light-matter coupling. As a result, the SHG in these photonic nanostructures can be enhanced by several orders of magnitude as compared to the unstructured counterparts. Additionally, a versatile nonlinear homogenization approach is used to demonstrate the underlying physics of the large SHG enhancement induced by the bound states in the continuum. Applications to practical photonic nanodevices are also discussed.

A comparative study on nonlinear emissions from single dielectric and metallic nanoantennas

Circular dichroism (CD), yielding a different response upon illumination with light having opposite spin angular momentum, is opening the way for many new applications from telecommunications to sensing. Although this phenomenon is extremely weak in natural materials, metasurfaces (MS) considerably enhance CD. In comparison to the linear regime, CD in the nonlinear regime (NLCD), e.g. higher harmonic-generation for one circular light polarization with respect to the opposite one, may exhibit much higher contrast. To date, NLCD demonstrations are still limited to plasmonic structures; however nonlinear MS based on dielectric materials have the potential to yield high NLCD with superior conversion efficiencies than their plasmonic counterpart. In this work we design an asymmetric Si-based MS supporting a quasi-bound state in the continuum (quasi-BIC) with a quality (Q) factor of 105 that exhibits NLCD up to 99.9% in third-harmonic generation (THG). The optimization is performed with full-vectorial numerical simulations implemented in COMSOL Multiphysics. We observe that tuning MS mode interference allows selective linear and nonlinear circular dichroism. Our results show the potential of quasi-BIC in dielectric metasurfaces for simultaneously high NLCD and conversion efficiency thus opening new possibilities for holography, sensing, and optical telecommunication applications.

We realize a silicon metasurface supporting high-Q resonances and demonstrate its capability to control the third-harmonic diffraction through the power redistribution between third-harmonic diffraction orders.

Photonic spin Hall effect, i.e., splitting of opposite spin photons perpendicular to the incident plane of impinging light beam, is of great interest for modern photonics with its potential applications in such devices as beam splitters, demultiplexers by photonic spin degree of freedom, chiral molecule sensors, etc. Here, we report on numerical simulation and experimental detection of this effect in an array of densely arranged tilted silicon nanowires (SiNWs) of about 100 nm in diameter. We compared scattering of fundamental near-infrared radiation and the third harmonic (TH) generated in the structures. The latter case approves high sensitivity of nonlinear optical process to local fields within the structure, thus allowing us to probe the sub-wavelength evolution of photons in it. Numerical simulations of circularly polarized light scattering by a single SiNW and a group of 13 SiNWs used as a geometrical approximation of the real SiNW array indicate maintenance of helical modes in SiNWs for the light incident at an oblique angle to their axis. Helical guided-like mode structure in SiNWs evidences synthetic gauge field for photons resulting in its turn in asymmetric scattering diagram both for fundamental frequency and the TH. SiNWs were formed by means of metal-assisted chemical etching of (110) crystalline silicon (c-Si). They were tilted to the c-Si substrate at an angle of 45°. The array demonstrated significant linear light scattering preventing it from exhibiting of circular anisotropy. Nevertheless, experiment on the TH generation pumped by femtosecond laser pulses at 1250 nm has demonstrated significant difference in the TH signals for cases of left- and right-handed circularly polarized fundamental radiation. The effect was detected for oblique (60°) light incidence on SiNWs, whereas for the laser radiation propagating along the SiNWs or perpendicularly to them TH signal did not depend on the pump radiation photon helicity sign. Thus, we have demonstrated polarization-dependent routing of circularly polarized near-infrared radiation in a SiNW array, which is evidenced by different TH generation efficiencies in such structure in response to incident radiation with circular polarization of opposite signs.

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Hybrid perovskites attracted enormous attention as a new magic material and an exciting playground for optoelectronics and photonics. Particularly light emitting devices, LEDs have been broadly developed, which are usually multilayer devices. In this talk I present the advantages and new processes in a different type of architecture, known as single layer Light emitting electrochemical cells: SL-LEC. This concept is based on the dynamic formation of favorable internal p-i-n structure by ionic migration in electrical field of applied operation voltage of LEC. This ions that are moved we have added externally in small amounts as e.g. Li-ion salts to serve for differentiated migration, preserving the motion of internal ions of perovskite crystals. Blue electroluminescence is highly desired for emerging light-emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve. Here, we leverage CsPbBr3-xClx mixed-halide perovskites, polyelectrolytes, and a salt additive to demonstrate pure blue emission from single-layer light-emitting electrochemical cells (PeLECs). Substituting Cl into CsPbBr3 produced luminescence from green through blue. Polymer and LiPF6 inclusion were found to increase photoluminescence quantum yield, suppress halide segregation, induce thin-film smoothness and uniformity, and reduce crystallite size. Overall, these devices show superior performance among blue perovskite LEDs and general LECs. This approach produced blue electroluminescence peaked at 464 nm that surpassed standard benchmarks with a luminance maximum of 540 cd/m2 and stable operation under constant current driving. We also demonstrate guest-host single PeLEC with widely tunable emitted color.

Single walled carbon nanotubes (SWCNT) are known to demonstrate high optical nonlinearity. Saturable absorption with picosecond relaxation time and high thermal stability make them perfect candidate for implementation for passive mode-locking. In present work with discuss the application of aerosol synthesized SWCNT thin film for ultra-short pulse generation in the fiber laser. We show that nonlinear optical response of carbon nanotubes can be control by electro-chemical gating. With this technique we can tune the Fermi level position of the SWCNTs and change modulation depth of saturable absorption in a wide range. We demonstrate that it gives control over pulse generation regime and allows to switch between sub-picosecond mode locking generation and microsecond Q-switching. We also discuss the stability of SWCNT saturable absorber. By measuring the heating temperature of the saturable absorber inside the laser cavity by the Raman line shift, we show that primary mechanism degradation under high-power illumination can be different for carbon nanotubes embedded in polymer matrix and polymer-free carbon nanotubes.

Engineering nonlinear optical responses at the microscale is a key topic in photonics for achieving efficient frequency conversion and light manipulation. Gallium nitride (GaN) is a promising semiconductor material for integrated nonlinear photonic structures. In this work non-scanning far-field nonlinear optical microscopy is employed to study the whispering gallery modes in tapered GaN microwire resonators. We demonstrate the confinement of whispering gallery modes under near-infrared excitation with the photon energy close to half of GaN bandgap. Our results indicate the enhancement of yellow-green luminescence by whispering gallery modes in GaN microwire resonators. Such microwire resonators can be used as compact microlasers or sensing elements in photonic sensors.

In this article, we present results of experimental and computational analysis of growth processes for wurtzite nanowires on graphene substrate. It was found that the GaN nanowires on graphene substrate have nitrogen polarity. The DFT-based computational analysis was used to explain this experimental result. It was suggested that polarity discrimination occurs due to dipole interaction between the nanocrystal and pi-orbitals of the graphene sheet. This physical effect can be used for creation of high efficient optical and piezoelectric devices.

Semiconductor quantum dots (QDs) grown by epitaxial methods are considered as the basis for the development of advanced optical quantum technologies due to the ability of generation of triggered single photons with small spectral linewidth and fast radiative decay time. Extensive efforts have been devoted to producing single photons with a high degree of indistinguishability [1]. Indistinguishable single photons are attractive for implementation of quantum computing elements, such as quantum bits, which practically do not suffer from decoherence. An important challenge is to extend the single-photon source to multiple quantum bits, as required by different quantum information protocols such as boson sampling, quantum teleportation and quantum metrology. One of the approaches to their formation is the use of many independent QDs emitting photons identical in all parameters [2]. Another approach is based on the use of only one perfect QD, which emits with a high efficiency a sequence of single-photon pulses, which are then demultiplexed over N parallel channels [3]. Implementing N-photon circuits in this configuration requires streams of N mutually indistinguishable single photons far apart in emission time. In this work, we demonstrated the possibility of combining these two principles by creating high-quality single-photon sources, which in general allow integration within a single semiconductor chip. For this purpose, self-assembled InAs/GaAs QDs were grown by molecular beam epitaxy and placed in a columnar optical microcavity with distributed Bragg reflectors, possessing a relatively low Q factor. The experiment on measuring two-photon interference, performed in the Hong-Ou-Mandel scheme at various delays between two photons successively emitted under resonant coherent excitation of a single QD, showed the possibility of achieving up to 93% indistinguishability at a 250 ns delay. It is assumed that the use of such microcavity structures with a low Q factor and a sufficiently wide spectral resonance will simplify the precise tuning of the single-photon generation wavelength, which will make it possible to increase the number of parallel channels in the circuits of optical quantum computers by integrating several independent sources of indistinguishable photons with a degree of indistinguishability sufficient to effectively demultiplex the photon flux emitted by each source. M. V. Rakhlin thanks the Council on grants of the President of the Russian Federation. [1] X. Ding et al., Phys. Rev. Lett. 116, 020401 (2016). [2] E. B. Flagg et al., Phys. Rev. Lett., 104, 137401 (2010). [3] H. Wang et al., Nat. Photonics 11, 361–365 (2017).

Deterministic sources of single and indistinguishable photons are required for various applications in emerging quantum information technologies. A global quantum network may boost the computational power by enabling distributed quantum computing and allow for secure communication over long distances. Strict requirements to the physical platform are needed for these applications. All functional elements including a single photon source have to be integrated on-chip to allow for platform scalability. Furthermore, the single photon source has to operate with high efficiency, yield indistinguishable photons and emit at the telecom C-band wavelength standard to avoid frequency conversion. InAs/InP quantum-dot based active material monolithically integrated with the Si-photonics platform potentially satisfies all the requirements mentioned, including the emission wavelength in the telecom C-band. In this contribution we present an f InAs/InP quantum dot single photon sources on the Si. The quantum dot source possesses high purity of single photon emission up to 80 K and operates in the telecom C-band. We will discuss all relevant aspect related to epitaxial growth of quantum dots, device design and various methods for integration of III-V material to Si. Two main approaches exist for integration, wafer bonding and direct epitaxial growth, and we will provide recent results obtained by following both directions.

Carbon dots (CDs) – small crystalline or amorphous carbon-based nanoparticles – have recently attracted much attention as promising fluorescent materials for a wide range of applications, both in the biomedical fields and in optoelectronics [1]. One of their widely accepted advantages is the simplicity of the formation of highly luminescent CDs from a wide variety of organic precursors. At the same time, several recent studies on these chemically synthesized CDs raised questions about the nature of the resulting products [2]. Their strong fluorescence can arise due to the presence of molecular organic fluorophores, not necessary CDs, as was assumed in the earlier publications. On the other hand, purely carbon dot samples can be synthesized yielding CDs of different sizes; this synthetic approach has been demonstrated to be an effective way to tune their optical properties [3]. Color-tunable fluorescence of CDs with blue, green, yellow, orange, red and even near-infrared emission has been achieved, with the color depending on size of the π-conjugated domains in the CD graphitic core [4]. Very recently, we have extended the family of the light-emitting colloidal carbon nanoparticles towards carbon nanorods with linearly polarized emission [5], as well as to other rather exotic shapes such as nanobelts and nanorolls [6]. 1. C. J. Reckmeier, J. Schneider, A. S. Susha, A. L. Rogach. Luminescent Colloidal Carbon Dots: Optical Properties and Effects of Doping. Optics Express 2016, 24, A313. 2. Y. Xiong, J. Schneider, E. V. Ushakova, A. L. Rogach. Influence of Molecular Fluorophores on the Research Field of Chemically Synthesized Carbon Dots. NanoToday 2018, 23, 124. 3. Z. Tian, D. Li, X. Zhang, D. Zhou, P. Jing, D. Shen, S. Qu, R. Zboril, A. L. Rogach. Full-Color Inorganic Carbon Dot Phosphors for White Light Emitting Diodes. Adv. Opt. Mater. 2017, 5, 1700416. 4. N. V. Tepliakov, E. V. Kundelev, P. D. Khavlyuk, M. Y. Leonov, W. Zhu, A. V. Baranov, A. V. Fedorov, A. L. Rogach, I. D. Rukhlenko. sp2–sp3-Hybridized Atomic Domains Determine Optical Features of Carbon Dots. ACS Nano 2019, 13, 10737. 5. Y. Xiong, X. Zhang, A. F. Richter, Y. Li, A. Döring, P. Kasak, A. Popelka, J. Schneider, S. V. Kershaw, S. J. Yoo, J.-G. Kim, W. Zhang, W. Zheng, E. V. Ushakova, J. Feldmann, A. L. Rogach. Chemically Synthesized Carbon Nanorods with Dual Polarized Emission. ACS Nano 2019, 13, 12024. 6. T. Liang, E. Liu, M. Li, E. V. Ushakova, S. V. Kershaw, A. L. Rogach, Z. Tang, S. Qu. Morphology Control of Luminescent Carbon Nanomaterials: from Dots to Rolls and Belts. ACS Nano 2021, 15, 1579-1586.

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After the discovery of graphene in 2004 many two-dimensional (2D) materials have been found including hexagonal boron nitride (hBN). Besides enhancing the properties of 2D materials, hBN triggered a large number of research work because room-temperature quantum emitters have been discovered. However, the generation of these ultrabright quantum emitters is mostly uncontrolled and their microscopic origin remains elusive. Here, we present a novel generation process to create luminescent centres in hBN by irradiation engineering. We systematically study the density of luminescent centres at different irradiation energies and irradiation fluences (defined as the number of oxygen atoms per area). Increasing the irradiation fluence by ten results in a five-fold enhancement of the density. In combination with molecular dynamics simulations we clarify the generation mechanism, for the first time to the best of our knowledge. Furthermore, we infer that two defects are most likely generated, namely VNCB and VB-. Ab initio calculations of these defects show excellent agreement with experimental photoluminescence line shapes. The generation of quantum emitters by irradiation engineering is a step towards the controlled generation of quantum emitters in hBN. Furthermore, the presented irradiation engineering is wafer-scalable and could be adapted to other irradiating atoms or ions as well as other gapped 2D materials.

Taking graphene electronics out of the lab into real-life applications requires the development of large-scale, low-cost, and robust materials with superior properties than what is possible with incumbent conventional technologies. In this contribution, we tackle this challenge with the laser-driven integration of nanoparticles into polymer substrates with the simultaneous in-situ generation of graphene. Our results show the formation of a 3D graphene network interconnected with metal nanoparticles, with good electrical conductivity and mechanical and chemical stability. Electron microscopy results and elemental analyses show the integration of nanoparticles and the laser-induced graphene into the polymer surface. We will also discuss the fundamental mechanisms behind the laser-induced formation of these graphene-based nanostructures related to the original nanoparticle film acting as photothermal transducers. Photoelectron spectroscopy analysis, Raman spectroscopy results, and high-speed optical imaging confirm our hypothesis on the formation mechanism. The remarkable electrical and mechanical characteristics of these nanomaterials are exploited in several applications from sensors and smart implants to energy transduction and energy storage.

We demonstrate nearly spherical nanoparticles of tungsten disulfide (WS2) produced by femtosecond pulsed laser ablation of bulk target in deionized water. Structural and optical analysis reveals that produced nanospheres preserve the crystalline structure, high refractive index and support strong excitons and Mie resonances in the spectral range 400-700 nm, resulting in enhanced photothermal response probed by Raman spectroscopy

We present a diffusion-based simulation model and a theoretical approach based on non-Markovian kinetic equations for explanation of long time power-law decay of photoluminescence (PL) emission intensity in semiconductor nanoplatelets. The shape of emission curves is thus an outcome of interplay of recombination, diffusion and trapping of excitons. At short times the excitons diffuse freely following the normal diffusion behaviour. The emission decay is purely exponential and is defined by recombination. At long times the transition into the subdiffusive motion happens and the emission occurs due to the release of excitons from surface traps. A power-law tail for intensity is a consequence of the release. The crossover from one limit to another is controlled by diffusion properties. The approach reproduces the properties of experimental curves measured for different nanoplatelet systems.

In this work, we investigate the effect of narrowband collective absorption in metasurfaces consisting of strongly anisotropic weakly absorbing MoS2 nanoparticles and supporting the response of quasi-trapped modes. We show that such systems can be tuned to produce a narrow absorption peak at 1550 nm. By varying the orientation of the polarization of the incident wave, it is possible to change the Q-factor of the absorption resonance in the range from 140 to 310 and achieve an absorption efficiency of about 90% at a sensitivity of 360 nm / RIU.

Dipole antennas have recently been introduced and used for imaging of the human body and head at ultra-high field (UHF, > 7T). Array coils constructed using dipole elements provide a unique simplicity while offering comparable transmit (Tx) efficiency and SNR with the conventional surface loop design. While half-wave length dipole antennas (500mm in free space at 300MHz) can be used for body imaging, they must be substantially shortened for use in human head arrays. Such short dipoles are poorly loaded and often decoupled only to the level of ~ -10dB, which may be insufficient for optimal Tx-performance. Commonly, adjacent array elements are decoupled by circuits electrically connected to them. Placement of such circuits between distantly located dipoles is difficult. A recently proposed decoupling technique using passive dipoles is appealing because no galvanic connection is required. At the same time, passive dipoles of similar size to active dipoles can interfere destructively with the RF field of the Tx-array. Thus, further optimizations of both the dipole geometry and decoupling methods are required. In this work, we present developments of 8-element 7T and 9.4T dipole transceiver arrays, which use a novel type of dipole antennas, i.e. folded-end dipole. In this antenna design, both ends of the dipole, which carry the highest voltage and lowest current are bent away from the sample and folded. This reduces the voltage along the portion of the dipole located near the sample and makes the current distribution along it more uniform. As a result, both the longitudinal coverage and Tx-efficiency are improved. In addition, we evaluated several modified passive dipole designs for decoupling the proposed array. We demonstrated that the suggested passive dipoles not only minimize coupling between the adjacent folded-end active dipoles but also produce practically no destructive interference with the RF field of the array.

Metamaterials based on capacitively-loaded rings (CLRs) have the key advantage of providing three-dimensional isotropy when they are arranged in a cubic lattice, an essential property to image 3-D sources. CLR metamaterial lenses with negative permeability have the ability to increase the SNR of MRI coils. A CLR metamaterial lens works placed between a surface coil and the sample, producing an enhancement of the sensitivity of the coil. However, it also increases the noise in the coil due to the ohmic losses of the metallic rings of the structure. Nevertheless, the enhancement of the sensitivity of the coil is high enough to compensate the additional losses introduced in the coil by the metallic structure of the lens. The effect of these additional losses as a function of the structure of the lens and the field strength was investigated. Moreover, CLR metamaterial slabs with zero/high permeability can reject/confine the RF magnetic field in MRI systems and can help to locally increase the SNR. Together with the improvement of the SNR, imaging speed is among the most important considerations in MRI. Scan time reduction without the need of increased gradient performance is achievable in parallel MRI (pMRI). In pMRI, noise correlation between coils in an array is reduced if the field of view (FOV) of the coils are well separated. The ability of CLR metamaterial lenses to localize the FOV of MRI coils in an array and thus to reduce the noise correlation has been also investigated.

Imaging of subtle changes in hand structures is challenged by the limited image quality, especially at 1.5 T. Reduction of specific absorption rate in metamaterial-assisted 1.5 T MRI provides an opportunity to utilize efficient pulse sequences and to improve the quality of acquired images. This work is devoted to the assessment of potential improvements of slice selectivity and reducing a "slice cross-talk" artifact, using a fast spin-echo (FSE) pulse sequence together with a metamaterial-based coil. The slice selection in conventional T1-weighted FSE wrist imaging pulse sequences was modeled using a "Bloch Equations Simulator". Two types of pulses were compared: apodized SINC pulses (reference) common for clinical FSE, and optimized selective Shinnar–Le Roux (SLR) pulses constructed in the MATPULSE program. Regular and SLR-based FSE pulse sequences were tested in a phantom experiment with different gaps between slices to investigate the “slice cross-talk” artifact presence. Combining the utilization of the metamaterial-based coil with an SLR-based FSE provided 28 times lower energy deposition in a duty cycle, as compared to the regular FSE with a conventional transmit coil. When the slice gap was decreased from 100% to 0%, the “slice cross-talk” effect reduced the signal intensity by 16%-18% in the SLR-based FSE and by 23%-32% for the regular FSE. The use of SLR pulses together with the metamaterial-based coil allowed to reduce the "slice cross-talk" effect in contiguous FSE, while still being within the safe SAR limits.

Magnetic resonance (MR) imaging (MRI) and in vivo MR spectroscopy (MRS) imaging (MRSI) methods use 1H or X-nuclear (e.g., 2H, 13C, 17O, 23Na and 31P) provide important means for biomedical research and clinical diagnosis. MR methods commonly face a fundamental challenge: low intrinsic signal-to-noise ratio (SNR) owing to an extremely small energy difference between the excited and non-excited nuclide spins. A key mission of MRI technology development is to explore all possible ways to improve MR imaging SNR. The prevailing paradigms for gaining MRI/MRS SNR such for higher spatial and/or temporal resolution have been built upon the use of higher static magnetic field strength, with 7.0 and 9.4 Tesla (T) increasingly used for human studies, and higher fields of 10.5T (CMRR, University of Minnesota) and 11.7T (NIH Intramural Research and Neurospin Paris) human systems in the process of being developed. Such field strengths represent practically achievable limits for human studies. Going beyond these limits would require the use of superconducting wires that are prohibitively expensive and difficult to work with in human size magnets. Also, going significantly beyond these magnetic fields for human applications encounters fundamental safety limits due to high specific absorption rate (SAR) of radiofrequency (RF) power. The engineering approach that incorporates ultrahigh dielectric constant (uHDC) materials with a RF coil has shown new utility to effectively improve RF transmission efficiency ("B" _"1" ^"+" ) and reception field (B_1^-), thus, gaining detection sensitivity or SNR for various MRI applications. This talk introduces incorporating radiofrequency (RF) coil(s) with uHDC ceramic to largely improve RF transmission efficiency, detection sensitivity and SNR. We demonstrate the proof-of-concept results using the uHDC ceramic technology for X-nuclear MRS imaging applications of 17O nuclide at 10.5 Tesla (T), 23Na and 31P nuclides at 7T. We discovered a large, global denoising effect by the uHDC materials, which synergistically resulted in SNR improvement. Similar improvement could also be observed in 1H MRI application on a 1.5T clinical scanner. This robust and cost-effective technology presents an alternative approch to improve imaging sensitivity and resolution.

The defining property of a topological system is that it exhibits some physical property that is highly robust to perturbations, namely, it is topologically protected. In recent years, it has been demonstrated that such phenomena are not confined to the domain of condensed matter physics (for example, in the quantum and spin Hall effects), but rather can be found in other systems such as photonics, ultracold atoms, acoustics, polaritonics, etc. In this talk I will present our experimental results on the effect of nonlinearity on topological photonic systems. First, I will show the observation of edge solitons, and the implications of nonlinearity upon them. Next, I will demonstrate how nonlinearity can act to quantize transport in photonic Thouless pumps, despite the absence of perfect band filling. Nonlinearity is a close cousin of interparticle interactions for bosonic systems, so we expect our results to be widely applicable beyond photonics.

In this talk we will discuss topological modes and related states which can occur on antiphase boundaries in photonic crystals as well as chiral structures in both two and three dimensions. We will discuss recent work on using real space techniques for analyzing defects and cavities, as well as artificial intelligence-based approaches for designing them. Practical applications will also be explored, such as couplers to conventional waveguides, and topological antennas.

This talk will summarize our recent results on nonlinear effects in topological waveguide arrays with self-action nonlinearity. We demonstrate different regimes of spatial modulational instability depending on the beam intensity and topological phase in a chiral square lattice. A continuum model formalism is developed to describe nonlinear dynamics of bulk modes and edge wavepackets guided directionally by topological domain walls. Our findings are generic to the systems governed by Dirac-like Hamiltonians and validated by numerical modeling in the framework of paraxial optics in periodic media.

In this talk I will discuss our invention of topological lasers and discuss unique applications that they may enable. I will also discuss the implementation of exceptional points with plasmons using the notion of complex hybridization and how we overcame immuno-assay nanosensing record with plasmon by more than two orders of magnitude.

Topological phases feature robust edge states that are protected against the effects of defects and disorder. While most topological phases rely on conservative, or Hermitian, couplings, recent theoretical efforts have combined conservative and dissipative couplings to propose new topological phases for ultracold atoms and photonic amplifiers. However, the topological phases that arise due to purely dissipative couplings remain largely unexplored. We realize dissipatively coupled manifestations of two prominent topological models, the Su-Schrieffer-Heeger (SSH) model and the Harper-Hofstadter (HH) model, in the synthetic dimensions of a time-multiplexed photonic resonator network. We observe the topological edge states of the SSH and HH models, measure the SSH model’s band structure, and induce a topological phase transition between the SSH model’s trivial and topological phases. In stark contrast with conservatively coupled topological phases, the topological phases of our network arise from bands of dissipation rates that possess nontrivial topological invariants (i.e. topological dissipation), and the edge states of these topological phases exhibit isolated dissipation rates that occur in the gaps between the bulk dissipation bands. Our results showcase the ability of dissipative couplings to break time-reversal symmetry: a phenomenon that enables us to realize nonzero Chern numbers with an effective magnetic field. We expect that our demonstration of robust topological edge states with isolated dissipation rates may inspire new designs for open quantum systems and photonic devices such as mode locked laser and optical computing architectures. Moreover, our time-multiplexed network, with its ability to implement multiple synthetic dimensions, dynamic and inhomogeneous couplings, and time-reversal symmetry breaking synthetic gauge fields, offers a flexible and scalable architecture for future work in synthetic dimensions.

Spin is one of the interesting phenomena that is inherent to photons as well as electrons in which plethora of analogies have been made from the electronic systems to the photonic systems that increased our understanding of both systems. One of these analogies is the quantum spin-hall effect (QSHE) which has led to the discovery of topological insulators. It was recently proved that evanescent waves as well possess intrinsic transverse spin that is dependent on the direction of propagation, which is also known as spin-momentum locking. This has enabled the control of the directionality of light based on its transverse spin direction by engineering metasurfaces and waveguides. The spin of the evanescent wave is defined as the direction perpendicular to the plane of electric and/or magnetic field rotation. The spin-dependent propagation of surface waves has enabled new applications such as unidirectional waveguiding using homogeneous surfaces without the complexity of topological insulators. Additionally, applications in optical devices such as polarization-based beam splitters and spin-dependent couplers became possible using such surfaces. In this work, we study a waveguide design consisting of C-shaped metallic posts that possess extrinsic chirality. We show that due to the symmetric dipole-dipole coupling introduced in the supported mode, it provides stronger transverse spin regions and hence higher spin-dependent directionality. We study the proposed waveguide design by calculating the directionality ratio as well as the spin density. We show that the designed waveguide achieves a directionality ratio of about 95%. We also study the effect of placing different local defects on the directionality of the supported guided mode. We report that the chiral waveguide mode is less sensitive to scaling defects and defects placed at the sides of the waveguide while it is more sensitive to defects placed at the center as well as defects that flip the spin direction such as metallic blocks.

Nowadays, hollow-core photonic crystal fibers are widely used in optics, since their linear and nonlinear optical properties are highly tunable [1]. However, a thorough theoretical formulation for the pulse propagation in such fibers has been missing so far due to the leaky nature of the occurring modes. We have recently derived such a formulation that is capable of treating guided and leaky modes based on the so-called resonant-state expansion with analytical mode normalization [2]. For leaky modes, we find that the Kerr nonlinearity parameter has an imaginary part that provides either nonlinear gain or loss for overall attenuating pulse that can significantly influence the pulse dynamics with intense pulse compression and spectral broadening in the case of nonlinear gain. Our theory can be extended to parametric processes such as degenerate four-wave mixing [3]. [1] F. Benabid and P. J. Roberts, J. Mod. Opt. 58, 87 (2011). [2] I. Allayarov et al., Phys. Rev. Lett. 121, 213905 (2018). [3] I. Allayarov et al., Phys. Rev. A 101, 043806 (2020).

TBA

Recent development of non-Hermitian photonics revealed the unique properties possessed by the so-called PT-symmetric optical structures characterized by the balanced distribution of loss and gain. We study the regularities of spontaneous PT-symmetry breaking in the simple trilayer structure with the outer loss and gain layers consisting of materials with permittivity close to zero. We find the singular points in the dependence of the loss and gain level necessary for PT-symmetry breaking on the light frequency and incidence angle. These singular points provide a new mechanism for the quasi-bound state in the continuum manifestation due to PT-symmetry breaking with the loss and gain value serving as an asymmetry parameter.

Using scattering matrix formalism we derive analytical expressions for the eigenmodes of a composite structure consisting of two dielectric diffraction gratings with Lorentzian profile in reflection. Analyzing these expressions we prove formation of two distinct pairs of exceptional points, provide analytical approximations for their coordinates and by rigorous simulation demonstrate eigenmodes interchange as a result of encircling said exceptional points.

Random numbers are a key component for applications such as Monte Carlo simulations, cryptography, gambling applications, etc. The development of hardware random number generators (RNGs) is being actively pursued. In quantum RNG (QRNG) the impossibility of predicting the values of a physical quantity is based on the probabilistic nature of quantum processes. Recently, QRNG based on the phase noise of laser radiation, which provides several GHz rates of bit generation, was proposed. In this work, we use Maxwell-Bloch equations with Langevin noise terms in order to describe the dynamics of laser and random changes in laser radiation phase. As a result, we built a simple model that describes the generation of random numbers. This model allows the use of parameter values typical for various laser sources. And also the model can be extended to the dynamics of anapole nanolaser. We expect that the employment of an anapole nanolaser will improve the characteristics of the QRNG in terms of footprints, energy consumption, stability, and price.

Two-dimensional metal halide perovskites are novel materials that have attracted great interest for the development of next-generation optoelectronic devices due to their outstanding figures of merit in photovoltaic solar cells, and in light-emitting devices, which come along with high defect tolerance, low-cost solution processing and tunable emission across the visible spectrum. They consist of alternating organic and inorganic layers, and this highly anisotropic architecture provides unique elastic, dielectric, and optoelectronic properties that lead to peculiar phenomena, such as self-trapping of excitons due to local lattice distortions. Furthermore, the strong confinement of the charge carriers in the inorganic layers makes such structures natural quantum wells that are appealing for fundamental research and photonic applications. Recently, our group demonstrated how the choice of the type of organic molecules can be exploited to engineer the optical properties of these 2D materials.1-4 Here we present a systematic study of their photophysics and vibrational properties at room and cryogenic temperatures. We find that the self-trapped exciton emission strongly depends on the organic cation type and temperature, and that the rich spectrum of vibrational resonances is governed by the organics that determine the distortions of the single octahedra layers. References 1. B. Dhanabalan, G. Biffi, A. Moliterni, V. Olieric, C. Giannini, G. Saleh, L. Ponet, M. Prato, M. Imran, L. Manna, R. Krahne, S. Artyukhin, M. Arciniegas, Adv. Mater. 2021. 2. B. Dhanabalan, A. Castelli, M. Palei, D. Spirito, L. Manna, R. Krahne, M. Arciniegas, Nanoscale 2019, 11, 8334-8342. 3. B. Dhanabalan, Y.-C. Leng, G. Biffi, M.-L. Lin, P.-H. Tan, I. Infante, L. Manna, M. P. Arciniegas, R. Krahne, ACS Nano 2020, 14, 4689-4697. 4. B. Dhanabalan, . D. Pothuraju, S. Marras, L. Pasquale, L. Manna, R. Krahne, M. Arciniegas, Adv. Photon. Res.2021.

Photoelectric effects in 2D materials have been actively studied in recent years aimed at the development of photodetectors and energy harvesting devices [1]. Various mechanisms are responsible for generation of the dc electric current under illumination of a 2D structure with electromagnetic radiation. Among them the photogalvanic effect is of particular interest, since the corresponding photocurrent is formed on a small (ps-) scale, determined by the momentum relaxation of charge carriers. In the bulk of 2D crystals the photocurrent related to the photogalvanic effect arises due to the lack of space-inversion center in the crystal lattice and is absent or small in centrosymmetric crystals, such as graphene. However, space inversion symmetry is broken naturally at the edges of 2D materials leading to generation of the photocurrent, which flows along the structure edges and is absent in the bulk. Such edge photocurrents were observed in doped single- and bilayer graphene [2,3,4] and were related to the rectification of the bulk ac current, induced by the electric field of the wave, at the edge [3,5]. With increasing the frequency of the incident radiation optical transitions between valence and conduction bands come to play leading to another mechanism of the edge photocurrent generation, possibly, with larger magnitude. Here we study the edge photogalvanic effect (EPGE) in 2D materials caused by direct optical interband transitions. The edge photocurrent emerges due to the alignment of charge carrier momenta by linearly polarized electromagnetic wave with a subsequent scattering of the carriers at the edge and consists of electron and hole contributions. The mechanism of edge current formation is reminiscent of the surface photogalvanic effect studied at the surfaces of bulk semiconductor crystals and metal films [6, 7]. We develop a microscopic theory of the EPGE for a large class of 2D materials with the gapped or gapless Dirac-like energy spectrum, such as monolayer and bilayer graphene, monolayers of TMDC, HgTe/CdHgTe quantum wells with close-to-critical thickness, etc. In 2D Dirac materials, the optical alignment of carriers can be pronounced, compared to traditional quantum wells, giving rise to large photocurrent. We show that the current is controlled by the radiation polarization, its magnitude reaches 1 nA per W/cm2 of the radiation intensity for a single edge and can be enhanced to 1 A in a ratchet-like structure consisting of multiple narrow strips. We also investigate the effect of a static magnetic field applied normally to the 2D plane and show that the field modifies the polarization dependence of the currents and introduces additional imbalance between the electron and hole currents. Taking into account the important role of edge regions in micro- and nano-scale devices, we expect that the EPGE can determine the photoresponse of small-size devices and find applications in detectors of terahertz and infrared radiation and radiation polarization [8]. 1. F. H. L. Koppens et al., Nat. Nanotechnol. 9, 780 (2014). 2. J. Karch et al., Phys. Rev. Lett. 107, 276601 (2011). 3. S. Candussio et al., Phys. Rev. B 102, 045406 (2020). 4. S. Candussio et al., Phys. Rev. B 103, 125408 (2021). 5. M. V. Durnev and S. A. Tarasenko, Phys. Stat. Solidi (b) 258, 2000291 (2021). 6. L. I. Magarill and M. V. Entin, Sov. Phys. Solid State 21, 743 (1979). 7. V.L. Alperovich et al., Sov. Phys. JETP 53, 1201 (1981). 8. M. V. Durnev and S. A. Tarasenko, arXiv:2011.10070.

The photoluminescence and nonlinear transmission of atomically thin population of colloidal CdSe rolled-up nanosheets were investigated at the one-photon stationary excitations of excitons by the third harmonic of Nd3+:YAP laser pulses. It was revealed that the nonlinear optical response of the nanoscrolls is strongly influenced by multiwalled rolled-up structure. The broadening of exciton band and the red shift of the photoluminescence were observed and explained by coupling effect within the folded scroll-layers.

Molybdenum disulfide (MoS2) is a layered material of transition metaldichalcogenides with a high refractive index in the visible and infrared spectral range. Thismaterial has a strong non-linear optical properties at the monolayer form due to the lack ofinversion symmetry. Here, we show enhanced second harmonic generation from MoS2nanodiskresonator due to the overlap of Mie-type resonances at the fundamental wavelength with theC-exciton resonance at the second-harmonic wavelength.

We demonstrate that four-spin interactions can cause a phase transition from a collinear state to a non-collinear magnetic ground state (such as magnetic vortices or magnetic skyrmions) in crystals with D3h point group of symmetry, where all two-spin chiral terms are forbidden by symmetry. Such crystals rather common among two dimensional magnets. The corresponding non-collinear ground state may also be additionally stabilized by an external magnetic field. Taking into account possible four-spin chiral exchange interactions is important for understanding noncollinear magnetic order in these systems. We also address a possible stabilization of bimerons by the same contribution.

The properties of screening effect for energy spectrum of excitons in monolayer transition metal dichalcogenides are investigated using a multiband model. The excitonic hamiltonian in the product base of the Dirac single-particle is used. The corresponding energy eigenvalue system of the first order ODE (radial equations) was solved using the finite difference method. This enables to determine the energy eigenvalues of the discrete excitonic spectrum and the wave functions. We compare the results for the energy spectrum and the corresponding eigen-functions forms for $WS_2$ and $WSe_2$ computed for two different potentials: pure Coulomb and screened Coulomb (Keldysh potential). It is demonstrated that excitonic energy levels for unscreened potential lie dipper, and the corresponding eigen-functions' forms differ from those obtained for screened one.

Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by huge oscillator strengths. Encapsulation of monolayers such as MoS$_2$ or MoSe$_2$ in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. The encapsulation affects the light-matter interaction and, accordingly, the exciton radiative lifetime and the electron-hole long-range exchange interaction. In this work we demonstrate the control of these two key properties of excitons in atom-thin semiconductors. We show that the exciton radiative rate in van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. Our calculations based on the transfer matrix formalism show that depending on the thicknesses of surrounding layers the exciton emission time can be either increased by a factor of $4$ or reduced by several orders of magnitude. The theory is confirmed by the experiments performed on MoSe$_2$ monolayers. The fit of the experimental data allows to establish the oscillator strength of the exciton resonance [1]. The exciton valley dynamics in van der Waals heterostructures with transition metal dichalcogenide monolayers is driven by the long-range exchange interaction between the electron and the hole in the exciton. Its physical origin is the virtual recombination and generation of the electron-hole pairs in opposite valleys $\mathbf K_+$ and $\mathbf K_-$. The exchange interaction couples the states active in the opposite circular polarizations resulting in the longitudinal-transverse (LT) splitting of excitons propagating in the monolayer plane. The exciton LT splitting acts as a driving force of its valley dynamics. We study theoretically the effect of the dielectric environment on the long-range exchange interaction and demonstrate how the encapsulation in hBN modifies the exciton longitudinal-transverse splitting. We calculate the exciton spin-valley polarization relaxation due to the long-range exchange interaction and demonstrate that the variation of the monolayer environment results in significant, up to fivefold, enhancement of the exciton valley polarization lifetime [2]. We also discuss valley polarization fluctuations of excitons in van der Waals heterostructures due to an interplay of the LT splitting and interactions. M.A.S. was supported by the Russian Science Foundation project No. 19-12-00273. References [1] H.H. Fang, B. Han, C. Robert, M.A. Semina, et al., Control of the Exciton Radiative Lifetime in van der Waals Heterostructures, Phys. Rev. Lett. 123, 067401 (2019). [2] A. I. Prazdnichnykh, M. M. Glazov, et al., Control of the exciton valley dynamics in atomically thin semiconductors by tailoring the environment, Phys. Rev. B 103, 085302 (2021).

Magnetic resonance imaging (MRI) relies on a precise control of spin magnetic moments in the body tissues. To achieve such control, one needs to induce a uniform radiofrequency (RF) magnetic field flux (B1+) across the imaged volume. In 7T MRI scanners, the proton (1H) Larmor frequency reaches 300 MHz. Due to the high relative permittivity of human tissues, the associated RF wavelength can shrink down to 11 cm, which is comparable to the dimensions of some human organs. Consequently, spatially varying phase and amplitude of the RF fields generate signal inhomogeneities across the image. For head imaging, signal losses become strongly visible in the temporal lobes and cerebellum regions of the brain. Different approaches have been implemented to improve B1+ field uniformity of transmit coils such as passive and active RF shimming. Active RF shimming is based on coils with multiple independently controllable transmit elements or channels. These additional degrees of freedom can be exploited to mitigate B1+ inhomogeneities. But, it raises challenges in terms of workflow and patient safety (specific absorption rate). In contrast, passive RF shimming relies on the insertion of passive structures between the subject and the coil. Devices based on high-permittivity dielectric materials and/or metamaterials have seen strong development in the past years. Induced currents (displacement or conduction currents) generate a secondary RF field that corrects the initial B1+ field. This talk will review some of the achievements and remaining challenges of RF passive shimming in high field MRI applications. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 736937 first (M-CUBE project), and then under grant agreement No 952106 (M-ONE project).

This work aims to provide a way of performing parallel imaging with a single-channel variable-frequency resonant device. Different spatial sensitivity profiles required for SENSE reconstruction are achieved by switching between the device eigenmodes. A device capable of such switching is manufactured and several k-spaces are acquired using the device different eigenmodes. The k-spaces are then subject to downsampling to obtain the sensitivity profiles of each eigenmode and then - to perform SENSE-based reconstruction of the unaliased images with different acceleration factors.

We present the initial experimental results obtained using a two-part receive/transmit (Rx/Tx) radiofrequency (RF) coil design for small animals magnetic resonance imaging at 7 T. The assembly uses a butterfly-type coil tuned to 300 MHz for scanning the 1H nuclei and a non-resonant antenna with a metamaterial-inspired resonator tunable over wide frequency range for X-nuclei. 1H, 31P, 23Na and 13C are selected as test nuclei in this work. Coil simulations show the two parts of the RF-assembly to be efficiently operating at the required frequencies. Simulations and phantom imaging show sufficiently homogeneous transverse transmit RF fields and tuning capabilities for the pilot heteronuclear experiments.

Radiofrequency (RF) magnetic field inhomogeneity is a significant concern in imaging large fields of view at 3 T magnetic field imaging (MRI). The wavelength of the RF field gets shortened to ~26 cm when measured in the body. It leads to the constructive or destructive interference of the RF magnetic field, and as a result, to the appearance of local areas of the signal where it gets brighter or darker [1]. High-permittivity dielectric pads [2], consisting of ceramic powders mixed with heavy water, have been shown to increase the RF magnetic field in low-transmit efficiency regions at high and ultra-high magnetic fields. However, dielectric pads have some drawbacks: their material parameters can change with time, they may contain not bioincompatible components, and they have considerable weight (several kg) [3]. Recently, an artificial dielectric slab that mitigates dielectric pad disadvantages has been shown feasible for parietal lobes imaging at 7 T [4]. However, the proposed artificial dielectric slab was rigid and operated in only one position to the head (parallel to the axial plane). Here, we propose the ultralight and flexible metasurface to improve abdominal imaging at 3 T. The metasurface constitutes a grid of metal wires loaded with capacitances printed on a flexible printed circular board substrate. Numerical studies and in vivo imaging of a healthy volunteer with the proposed structure showed the same increase in the transmit RF field distribution at the area of interest as for conventional dielectric pads. Also, unlike conventional dielectric pads, the metasurface based pad weighs less than 100 g, and it will last longer in working order. The proposed topology and the explained design procedure can be adopted for replacing dielectric pads with different thickness and permittivity values used in other imaging tasks at different static fields. References: 1. Christianson KL et al. Duke Review of MRI Principles: Case Review Series. 2012. 2. Teeuwisse WM et al. Simulations of high permittivity materials for 7 T neuroimaging and evaluation of a new barium titanate-based dielectric. Magn Reson Med. 2012;67(4): 912-918. 3. Neves AL et al. Compressed perovskite aqueous mixtures near their phase transitions show very high permittivities: New prospects for high-field MRI dielectric shimming. Magn Reson Med. 2018;79(3): 1753-1765. 4. Vorobyev V et al. An artificial dielectric slab for ultra high-field MRI: Proof of concept. Journal of Magnetic Resonance. 2020; 320: 106835.

Semiconducting monolayer crystals have emerged as a new platform for studies of tightly bound excitons and many-body excitations in ultimately thin materials. Their giant dipole coupling to optical fields makes them very appealing for (nano-) photonic devices, and for fundamental investigations in the framework of cavity quantum electrodynamics. Our recent experiments reflect that the regime of strong light-matter coupling between excitons in atomically thin transition metal dichalcogenides and microcavity photons can be accessed, and the effect of bosonic condensation of exciton-polaritons, driven by excitons hosted in an atomically thein layer of MoSe2 has become within reach. We furthermore address the pending question on the emergence of long-range first-order spatial coherence, via interferometric g(1)(t) measures. I will finally discuss the emergence of polaritonic resonances at room temperature in fully tuneable optical lattices with integrated WS2 monolayers as a first step towards exploring correlations in highly non-linear synthetic lattices

New-generation nonlinear planar polaritonic devices based on 2D semiconductors demonstrate great potential for a wide range of practical applications. In this work, we experimentally study strong light–matter coupling between waveguide photons and excitons in a photonic system based on dielectric slab waveguides integrated with 2D transition metal dichalcogenides.

Recent discoveries have shown that when two layers of van der Waals (vdW) materials are superimposed with a relative twist angle between their respective in-plane principal axes, the electronic properties of the coupled system can be dramatically altered. Here, we demonstrate that a similar concept can be extended to the optics realm, particularly to propagating polaritons – hybrid light-matter interactions –. To do this, we fabricate stacks composed of two twisted slabs of a polar vdW crystal (α-MoO3) supporting low-loss anisotropic phonon polaritons (PhPs), and image the propagation of the latter when launched by localized sources (metal antennas). Our images reveal that under a critical angle the PhPs isofrequency curve (determining the PhPs momentum at a fixed frequency) undergoes a topological transition. Remarkably, at this angle, the propagation of PhPs is strongly guided along predetermined directions (canalization regime) with no geometrical spreading (diffraction-less). These results demonstrate a new degree of freedom (twist angle) for controlling the propagation of polaritons at the nanoscale with potential for nano-imaging, (bio)-sensing, quantum applications and heat management.

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Our study reveals that high-Q modes in subwavelength resonators can be formed due to strong interaction of two leaky modes, which interfere destructively resulting in strong suppression of radiative losses. This clearly confirms that such states are governed by the physics of bound states in the continuum. We believe that our work opens novel opportunities for subwavelength doptics and nonlinear nanophotonics.

Surface electromagnetic waves, propagating along the interface of two dissimilar media, have been the subject of extensive research during the last decades because they represent one of the fundamental concepts of nanophotonics. Dyakonov surface waves are a family of surface waves that exist at the interface of two media at least one of which is a dielectric with positive anisotropy as predicted in 1988 in [1]. In this pioneering work, Dyakonov surface waves have been considered at a flat and infinite interface. In our works [2,3] we theoretically study Dyakonov-like surface waveguide modes (DSWMs) that propagate along the planar strip of the interface between two uniaxial dielectrics. We demonstrate that due to the one-dimensional electromagnetic confinement, DSWMs can propagate in the directions that are forbidden for the classical Dyakonov surface waves at the infinite interface. We also report that due to the specific boundary conditions of the strip waveguide, DSWMs can exist even in case of dielectrics with negative anisotropy. [1] D’yakonov, M. I. (1988). New type of electromagnetic wave propagating at an interface. Sov. Phys. JETP, 67(4), 714-716. [2] Chermoshentsev, D. A., Anikin, E. V., Dyakov, S. A., & Gippius, N. A. (2020). Dimensional confinement and waveguide effect of Dyakonov surface waves in twisted confined media. Nanophotonics, 9(16), 4785-4797. [3] Anikin, E. V., Chermoshentsev, D. A., Dyakov, S. A., & Gippius, N. A. (2020). Dyakonov-like waveguide modes in an interfacial strip waveguide. Physical Review B, 102(16), 161113.

We propose a simple integrated resonant structure for the Bloch surface wave platform, which consists of two subwavelength grooves patterned on the surface of a one-dimensional dielectric photonic crystal. We demonstrate that the investigated structure can operate in a parasitic-scattering-free regime and, in this case, provide unity transmittance and zero reflectance at resonance conditions associated with the excitation of a leaky mode of the structure localized at the central ridge formed by the grooves. The proposed structure may find application in integrated photonic devices for optical filtering and analog optical computing.

Uploaded a short abstract file.

The photonic crystal slabs structures with high-Q resonances play important role in modern nanophotonics. They are responsible for strong increase of local light intensity and determine the major properties of linear and nonlinear effects in this domain. Regular arrays of metallic nanoparticles on dielectric waveguides form an important class of resonant metal dielectric systems. In this talk I present the new and efficient method to calculate the resonances in these structures and demonstrate its ability to describe spectral and angular dependencies of their polarization properties. The method is based on the splitting of structure in two parts that alone do not support the resonances and tracing the phase of the resonant denominator in the scattering matrix of the combined system. This phase based expansion appears to provide much better approximation for the scattering matrix near the resonance compared to the conventional frequency based resonant terms.

Semiconductor nanocrystals have attracted great interest for color conversion and enrichment in quality lighting and displays. These span a variety of types and structures from colloidal quantum dots to the latest family of nanocrystals, the atomically-flat colloidal quantum wells (CQWs). In this talk, we will introduce the emerging field of semiconductor nanocrystal optoelectronics employing tightly-confined, quasi-2-dimensional CQWs, also popularly nick-named ‘nanoplatelets’ with recent examples of their photonic structures and optoelectronic devices. Different demonstrations, which will be presented in this talk, using these CQWs include record high optical gain coefficients, gain thresholds at the level of sub-single exciton population per CQW on the average, ultrathin optical gain media and lasers, record high-efficiency colloidal LEDs utilizing the CQWs as the electrically-driven active emitter layer, and record low-threshold solution lasers using the same CQWs employed as the optically-pumped fluidic gain medium.

Semiconductor quantum dots are one of the best on-demand sources of single and entangled photons to date, simultaneously merging the highest brightness and indistinguishability of the emitted photons. They are, therefore, among the strongest candidates for practical single-qubit quantum photonic devices. However, to exploit the full advantage of quantum physics, multi-qubit photonic devices are vital. This talk will present our approach for realizing practical multi-qubit photonic devices for quantum networks based on novel crystal-phase quantum dots in nanowires.

The undoubted advantage of light-emitting SiGe heterostructures for Si-based photonics is their compatibility with modern CMOS technology. However, until now, the efficiency of such sources remains significantly lower than that of sources based on direct-gap A3B5 materials. The approaches to increasing the efficiency of light sources based on SiGe heterostructures, which include both optimization of the active medium (SiGe heterostructures) itself and the use of various dielectric micro- and nanoresonators will be considered in talk. Tensile strained Ge microstructures and structures with Ge(Si) self-assembled nanoislands and quantum dots (QDs) are considered as an active medium. Optimal growth conditions and doping level for achievement of the maximum luminescence intensity at room temperature for both types of structures were determined [Semicond. Sci. Technol. 26, 014029 (2011); Semicond. Sci. and Technol. 33, 124019 (2018)]. The advantages of structures with Ge(Si) nanoislands as an active medium in micro- and nanoresonators was demonstrated [Nano Letters 17, 6886 (2017); Semicond. Sci. and Technol. 34, 024003 (2019); ACS Photonics 8, 209 (2021); arXiv preprint arXiv:2006.06086]. Various approaches to increasing the intensity of the luminescence from spatially ordered Ge(Si) QDs by incorporating them into two-dimensional photonic crystals are considered [Semiconductors 53, 1329 (2019); Semiconductors 54, 853 (2020)]. The possibility of achievement of the stimulated emission in locally tensile strained n-Ge microstructures through improvement of heat sink [Semiconductors 53, 1324 (2019)] and embedding into different resonators will be discussed.

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We demonstrate growth of AlGaAs NWs with GaAs QDs and InP NWs with InAsP QDs on silicon substrates. Results of GaAs QDs optical properties study have shown that these objects are sources of single photons. In case of InP NWs with InAsP QDs, the results we obtained indicate that nearly 100% of coherent NWs can be formed with high optical quality of this system on a silicon surface. The presence of a band with maximum emission intensity near 1.3 μm makes it possible to consider the given system promising for further integration of optical elements on a silicon platform with fiber-optic systems. Our work, therefore, opens new prospects for integration of direct bandgap semiconductors and single-photon sources on silicon platform for various applications in the fields of silicon photonics and quantum information technology.

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In this work we consider the classical analog of the FRET to characterize the effect of the environment. Usually, emitters in the microwave are designed to provide a desired far-field pattern at much larger distances than the wavelength, but near-field patterns are typically harder to control even for elementary sources. In this work, we perform analytical calculations and measurement of the energy transfer of the simple system of two dipoles near a conductive plane in the microwave range. We consider two cases of dipole orientations to the conductive plane: parallel and perpendicular to the conductive plane. We develop an analytical model to calculate the energy transfer ratio between the two dipoles with finite length near a conductive plane by calculation of mutual impedance of the dipoles. In the frequency range, 1.5 – 6 GHz for two short dipoles (10mm), the energy transfer ratio was measured using a vector network analyzer and compared with analytical results. The result was compared with an analytical model for calculating FRET from the Green function of the point dipoles at optical wavelengths. We show that accounting for finite length of dipoles gives better accuracy compared to the point dipole case and must be considered for precision measurements.

Electrically small dielectric antennas are of great interest for modern technologies, since they can significantly reduce the physical size of electronic devices for processing and transmitting information. We investigate the influence of the resonance conditions of an electrically small dielectric spherical antenna with a high refractive index on its directivity and analyze the dependence of these resonances on the effectively excited modes of the dielectric sphere.

We experimentally confirmed the dispersion properties of metamaterial consist of two orthogonal sets of metallic wires - so-called the double wire medium. This material has attracted significant interest of researchers since it has hyperbolic isofrequency contours in a wide frequency range and low-losses due to strong spatial dispersion. In this work, we find not only the shape of the isofrequency contours, but also estimate the experimental error relative to the numerical results obtained in CST eigenmode solver.

Electromagnetic scattering typically occurs when a change in the material properties is perceived by the propagating wave, that inevitably splits into a reflected and refracted wave to maintain the continuity of the field components at the interface between the two media. However, such a scattering phenomenon occurs also when the entire media suddenly switches its properties to other values at a certain instant of time, realizing the so-called temporal interface. After a temporal interface, a couple of waves, one reflected and one transmitted, starts to propagate in the new media with the same wavelength but at a different frequency. Exploiting the analogies and differences between spatial and temporal interfaces, in this contribution we present the temporal counterparts of conventional electromagnetic devices based on dielectric slabs and a cascade of them, i.e. the multilayered structures. In particular, we discuss about the analysis and design strategies for synthetizing the desired scattering response in both transmission and reflection and present the possible families of devices based on multi-switched temporal metamaterials that can be conceived.

Latency currently limits the most promising applications of electromagnetic imaging and sensing, including those built upon programmable metasurface hardware. In that respect, a fundamental caveat with the deployed compressed sensing techniques is that initially all information is indiscriminately multiplexed across a diverse set of measurement modes, and only during data processing one begins to select the information that is relevant to the task (e.g. concealed weapon detection). We introduce a “learned sensing” paradigm in which programmable meta-atoms are interpreted as trainable physical weights; together with the digital weights of the processing layer, the programmable meta-atoms are integrated into a hybrid analog-digital sensing pipeline empowered by machine learning, and jointly optimized. Thereby, the discrimination between relevant and irrelevant information can be made already during the measurement process. By illuminating the scene with the learned patterns, a remarkable improvement in latency is achieved compared to state-of-the-art compressed sensing approaches that leverage random patterns, orthogonal patterns or principal scene components. We discuss our recent numerical and experimental investigations of this approach. Finally, we briefly discuss to what extent the achievable resolution is limited by the wavelength.

Topological photonics offers an enhanced control over electromagnetic fields by providing a platform for robust trapping and guiding of topological states of light. By combining capabilities offered by topological photonics with strong light-matter interactions in polaritonic systems one can further expand possibilities to manipulate both light and matter degrees of freedom of these half-light half-matter quasiparticles, such as exciton polaritons in semiconductor heterostructures and 2D materials. Here we demonstrate that strong coupling between topological photons with another type of solid-state excitations – phonons in hexagonal boron nitride (hBN) – offers a new platform to control and guide hybrid states of light and lattice vibrations in a uniquely robust manner. Strong coupling between the bulk states of a topological metasurface and phonons in hBN leads to the formation of topologically nontrivial bulk polaritonic states characterized by nonvanishing pseudo-spin-Chern numbers, which gives rise to the emergence of helical phonon-polaritonic edge states. These topologically robust half-light and half-lattice vibration excitations are shown to be a pseudo-spin polarized and carry nonzero angular momentum locked to their propagation direction. The topological phonon-polariton platform therefore enables robust funneling of helical infrared phonons along arbitrary pathways and across sharp bends, thus offering unprecedented opportunities for applications, from Raman spectroscopy with structured phonons, to directional heat dissipation along topologically resilient heat sinks.

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Microcavities with embedded optically active materials allow to create exciton-polariton ondensates in the strong light–matter interaction regime. These condensates exhibit quantum fluid properties up to room temperature, and, when crystal-like lattices are imprinted in the cavity, they can be used to emulate and study solid-state physics toy models. Here, we use tunable nanoscale defect cavities supporting room–temperature zero-dimensional exciton-polariton condensation to form a nano-fabricated two-dimensional Lieb lattice with an organic polymer. We exploit the tunability of our open cavity to selectively condense into the s-, p- and d-lattice bands. Furthermore, we interferometrically measure long-range first-order coherence across the lattice and assess the influence of the disorder in the system. These are key first steps to investigate extended topological polariton systems at ambient conditions.

The mechanism of electron pairing induced by a circularly polarized off-resonant electromagnetic field is suggested and examined theoretically for various two-dimensional (2D) nanostructures. Particularly, it is demonstrated that such a pairing can exist in 2D systems containing charge carriers with different effective masses. As a result of the pairing, the optically induced hybrid Bose-Fermy system appears. The elementary excitation in the system are analyzed and the possible Bose-Einstein condensation of the paired electrons and the related light-induced superconductivity are discussed.

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We explore the tunneling transport properties of a quantum dot embedded in an optical microcavity and coupled to a semiconductor-superconductor one-dimensional nanowire (Majorana nanowire) hosting Majorana zero modes (MZMs) at their edges. Conductance profiles reveal that strong light-matter coupling can be employed to distinguish between the cases of highly nonlocal MZMs, overlapped MZMs, and quasi-MZMs. Moreover, we show that it is possible to access the degree of Majorana nonlocality (topological quality factor) by changing the dot spectrum through photon-induced transitions tuned by an external pump applied to the microcavity

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We propose and theoretically and numerically investigate integrated high-contrast diffraction gratings for surface electromagnetic waves. We consider two platforms for the on-chip gratings: surface plasmon-polaritons propagating along metal-dielectric interfaces and Bloch surface waves propagating along interfaces of photonic crystals. We demonstrate that the optical properties of the studied integrated gratings are qualitatively close to the ones of the conventional high-contrast diffraction gratings. If the “parasitic” out-of-plane scattering is suppressed, the reflectance and transmittance of the on-chip gratings are not only qualitatively, but also quantitatively close to the corresponding values of the conventional “free-space” gratings. The obtained results may find application in novel integrated optical circuits.

We study resonant optical properties of a guided-mode resonant grating, the period of which rapidly varies in the periodicity direction. Optical properties of this structure are investigated rigorously using the Fourier modal method and the scattering matrix formalism. We also propose a coupled-mode theory (CMT), which enables describing the reflected and transmitted field distributions. By simulating the diffraction of a plane wave by the considered structure, we demonstrate that it can be used as a linear variable filter (LVF). We also investigate how the line shape of the resonances depends on the period variation rate. The considered structures can find application in novel multi- and hyperspectral optical systems.

A superscattering structure is an efficient energy-mapping device that of particularimportance for various electromagnetic experiment methods, with potential sensing and energyharvesting applications. We study in this work the scattering cross-section of outgoing channelsin the irreducible and singular basis for an arbitrary shape scatterer. The superscatteringstatus is shown to occur within a single outgoing channel of an optimized cluster of cylinders,a forbidden mechanism in spherically symmetric Mie resonators.

We describe a generalized normal modal expansion (GENOME) for electromagnetic problems based on eigenpermittivity modes. We demonstrate that our method is significantly faster, more accurate and robust than other scattering and modal methods. As a demonstration, we demonstrate te strengths of our approach on te calculation of Green's tensor for periodic structures, thermal emission, photoluminescence and complex-shaped scatteres. }

Metamaterials form a widely studied class of subwavelength-period photonic crystals that might be considered artificial material. Excitingly, such structures might have material parameters that are not observed in natural crystals and therefore provide non-typical optical properties. Commonly, metamaterials' properties are found phenomenologically by fitting the experimental spectra or spectra calculated for photonic crystals. Also, simple analytical models are widely used, although they are typically very limited in applicability. Nevertheless, such approaches cannot ensure that the considered photonic crystals indeed perform as a material with declared properties for any angle of the incident light, thickness, and shape of the structure. In the presented study, we present the microscopical approach for the extraction of effective material parameters. The external field is applied to the considered structure via the corresponding currents in meta-atoms of the crystal. Subsequent calculation of the averaged multipole moments allows not just to obtain the dispersion of the eigenmodes propagating in the material but also to provide valid boundary conditions, which is maybe even more important. In particular, we demonstrate that the approach successfully copes with Mie resonances in crystals of optically-dense particles and correctly describes the most exciting resonances in optical constants. The talk is invited to be presented at the session organized by S.G. Tikhodeev and N.A. Gippius.

The decay of localized surface plasmons in metallic nanoparticles can result in the generation of energetic or “hot” electrons and holes. These carriers can be harvested and harnessed for applications in photovoltaics, photocatalysis and light sensing. To optimize hot carrier production in devices, a detailed theoretical understanding of the relevant microscopic processes, including light-matter interactions, plasmon decay and hot electron thermalization, is needed. In the first part of my talk, I will describe a material-specific theory of hot-carrier generation in metallic nanoparticles. This approach combines a classical description of the light field with a quantum-mechanical treatment of the electrons. Combining this approach with materials screening techniques has enabled the discovery of efficient photocatalysts based on bi-metallic core-shell nanoparticles. In the second part of my talk, I will describe our efforts to develop a fully quantum-mechanical description of plasmon decay which can be used to describe hot carrier generation in a nanoparticle with a single plasmon quantum.

A modern state of the growth of epitaxial SiC films on Si is presented by a new method of atoms substitution. An ideology of the new method of SiC synthesis on Si is stated and a comparison of the theoretical statements with the experimental results is provided. The method consists in replacing a fraction of atoms of the silicon matrix by the carbon atoms to form molecules of silicon carbide. It was experimentally discovered that the process of substitution of Si matrix occurs gradually without destroying its crystal structure. The film orientation is set therewith not only by the surface of the silicon substrate but by the crystal structure of the original silicon matrix. A comparison of the new method of growth with the classical methods of thin film growth is presented. The properties of the realized SiC layers are specified in detail. By the example of chemical interaction of CO gas with monocrystalline Si matrix, the mechanism of behavior of a broad class of heterogeneous chemical reactions between the gas phase and solid has been revealed. As a result of this has been described a new type of phase transitions in a solid phase with a chemical reaction conducted through an intermediate state. The implementation of this mechanism made it possible to obtain a new type of template - a substrate with buffer transition layers intended for growing wide-gap semiconductors on silicon such as AlN, GaN, and AlGaN. The formation of a new Si phase in the “semimetal” state at the SiC(111)/Si (111) interface is theoretically predicted and experimentally confirmed. The formation of Si in the “semi-metal” state at the SiC/Si (111) interface is associated with large, short-term (pulse time of the order of 10-5-10-4 sec.) “Squeezing pulses” during the transition of Si to SiC. It is shown that the compressive pressures arising in a thin boundary layer with a thickness of the order of several nanometers can reach values of the order of 200–250 GPa. Pressures of this magnitude lead to the formation of special, previously unknown optical, electrical, and magnetic properties of the SiC (111) / Si (111) interface. The work was carried out within the framework of the project of the Russian Science Foundation No. 20-12-00193.

The never‐ending struggle against counterfeit demands the constant development of security labels and their fabrication methods. This study demonstrates a novel type of security label based on downconversion photoluminescence from erbium‐doped silicon. For fabrication of these labels, a femtosecond laser is applied to selectively irradiate a double‐layered Er/Si thin film, which is accomplished by Er incorporation into a silicon matrix and silicon‐layer crystallization. The study of laser‐induced heating demonstrates that it creates optically active erbium centers in silicon, providing stable and enhanced photoluminescence at 1530 nm. Such a technique is utilized to create two types of anti‐counterfeiting labels. The first type is realized by the single‐step direct laser writing of luminescent areas and detected by optical microscopy as holes in the film forming the desired image. The second type, with a higher degree of security, is realized by adding other fabrication steps, including the chemical etching of the Er layer and laser writing of additional non‐luminescent holes over an initially recorded image. During laser excitation at 525 nm of luminescent holes of the labels, a photoluminescent picture repeating desired data can be seen. The proposed labels are easily scalable and perspective for labeling of goods, securities, and luxury items.

Using direct femtosecond-laser projection lithography in chemically synthesized CsPbBr3 perovskite microcrystals we demonstrate high-throughput fabrication of advanced binary microscale optical elements for nanofocusing and generation of high-order optical vortex beams. The obtained results highlight the CsPbBr3 microcrystals as a promising material for realization of various complicated 2D micro-optical elements and holograms that can be directly imprinted using non-destructive and practically relevant laser technologies.

The effect of the crystal lattice mismatch between single GaAs nanowire grown on Si substrate on the solar cell efficiency is studied. The study is performed by conductive atomic force microscopy (C-AFM) supported by numerical simulation. C-AFM I–V curves were measured for wurtzite p-GaAs NW grown on p-Si substrate under red (wavelength=650 nm) laser illumination. Numerical simulations were performed considering piezoresistance and piezoelectric effects. The analysis demonstrated the presence of the tensiled (2%) zinc blend insert at the NW/substrate interface due to mismatch between the crystal lattices. Strained insert at the interface changes a polarity of photogenerated current.

Conventional chemical synthesis methods for nanomaterials fabrication do not always provide precise reproducible synthesis with controllable physicochemical parameters. A better control over the resultant properties of nanomaterials can be achieved by scaling down the synthesis approach to the microlevel. This can be realized by means of microfluidics. In this work, a microfluidic approach is applied for the controllable synthesis of perovskite particles with defined cubic morphology. The structural characterization of perovskite particles is performed using scanning electron microscopy and X-ray diffraction. All the synthesized particles demonstrate photoluminescence.

In this work, we demonstrate the possibility of using mechanical Scanning probe lithography (m-SPL) for fabricating nanophotonic devices based on multilayered transition metal dichalcogenides (TMDCs). By m-SPM, we created a nanophotonic resonator from a 70-nm thick MoSe2 flake transferred on Si/Au substrate. The optical properties of the created structure were investigated by measuring microphotoluminescence. The resonator exhibits four resonance PL peaks shifted in the long-wavelength area from the flake PL peak. Thus, here we demonstrate that m-SPL is a high-precision lithography method suitable for creating nanophotonic devices based on multilayered TMDCs.

We establish a simple quantitative criterium for the search of new dielectric materials with high values of refractive index in the visible range. It is demonstrated, that for light frequencies below the bandgap, the latter is determined by the dimensionless parameter calculated as the ratio of the sum of the widths of conduction and valence bands and the bandgap. Small values of this parameter, which can be achieved in materials with almost flat bands, lead to dramatic increase of the refractive index. We illustrate this rule with a particular example of rhenium dichalcogenides, for which we perform ab initio calculations of the band structure and optical susceptibility and predict the values of the refractive index n > 5 in a wide frequency range around 1 eV together with comparatively low losses. Since currently there exist vast material databases containing the data on their band structures, the proposed criterion can be used for the automated search of the perspective candidates for the novel high-index materials for all-dielectric photonics. Our findings open new perspectives in search for the new high-index/low-loss materials for all-dielectric nanophotonics.

Diamond has emerged as a unique material for a variety of applications, both because it is very robust and because it has defects with interesting properties. One of these defects, the nitrogen-vacancy center (NV center), has a single spin associated with it that shows quantum behavior up to room temperature. Our group is harnessing the properties of single NV centers for high resolution magnetic sensing applications. In this talk, I will introduce the basic concepts and emerging applications of diamond-based quantum sensors. I will discuss the challenges in the fabrication of diamond probes and their integration into scanning probe microscopy (SPM) systems. I will then present some illustrative examples of applications in nanoscale magnetism, including the imaging of antiferromagnetic domains and domain walls, and the flow of current in graphene devices.

Van der Waals materials have emerged over the last decade as the new playground for quantum photonics devices. Among them, hexagonal boron nitride (hBN) is an interesting candidate, mainly because of its crystallographic compatibility with many different 2D materials, but also because of its ability to host optically active spin defects. We have recently reported [1] the optically detected magnetic resonance (ODMR) of spin-triplet negatively charged boron vacancies (VB-) in hBN and determined their spin-Hamiltonian parameters. Furthermore, we demonstrated the coherent control of VB- at room temperature and determined the relevant spin-relaxation times. [2] In this respect, sensors based on such color centres embedded in an intercalated hBN layer may be particularly attractive, since the distance between the sensor and the object to be sensed can be quite small. The influence of external stimuli (magnetic field, temperature, pressure, etc.) on this spin defect will be also discussed. [3] [1] A. Gottscholl, M. Kianinia, V. Soltamov, C. Bradac, C. Kasper, K. Krambrock, A. Sperlich, M. Toth, I. Aharonovich, V. Dyakonov, Nat. Mater. 19, 540–545 (2020) [2] A. Gottscholl, M. Diez, V. Soltamov, C. Kasper, A. Sperlich, M- Kianinia, C. Bradac, I. Aharonovich and V. Dyakonov. Science Adv., in press (2021) [3] A. Gottscholl et al. arXiv:2102.10890v1 [cond-mat.mtrl-sci]

At the heart of the main criteria for a qubit lie the long system coherence and fast access. Several prominent solid-state realizations fulfill these criteria by using the long-living qubits defined within the crystal structure while being optically accessible through the semiconductor optical bandgap. Some of such qubits are based on defect centers, like nitrogen- or silicon-vacancies in a diamond. These demonstrate a long-living spin coherence up to room temperature. On the other hand, these qubits have a comparatively slow initialization, which lies in the range of hundreds of nanoseconds. This study presents a system that takes advantage of the long spin coherence time of deep defect centers while maintaining ultra-fast optical access for spin initialization and readout. Our choice falls on the defect centers in ZnSe, which have decades of history and were typically seen as a detrimental factor. Here, we focus on one type of center, the zinc vacancy, introduced by ex-situ Fluorine implantation. We find that the primary source of spin relaxation is the interaction with surrounding nuclear spins. This relaxation channel is eliminated by using isotopic purification of ZnSe so that spin relaxation is dominated by the anisotropic exchange interaction (Dzyaloshinskii-Moriya interaction). In this case, we observe the long spin coherence times up to 100 ns at room temperature with the possibility of fast optical access through an excitonic transition of ZnSe. Additionally, the spin dephasing time remains almost unchanged (the same) in magnetic fields up to one Tesla, demonstrating a high homogeneity of the ensemble.

Lead halide hybrid organic perovskites attract increased attention due their promising applications, like high quantum efficiency and easy synthesis. Spin properties in such system are not studied in detail so far, but shows promising results [1]. In particular the spin related Landé g-factor shows a high variety for several perovkites. Spin Flip Raman and time resolved Kerr spectrospcopy experiments g-factors for electron and hole in range of 1.7 to 3.6 (electrons) and -1.2 to 0.8 (hole) were observed. An experimental and theoretical analysis is presented, giving a carrier spin g-factor systematic for the class of lead halide perovskites single crystals.

Color centers in nanodiamonds are promising candidates for the creation of high-speed sources of single photons without blinking and degradation. Color centers in high pressure-high temperature (HPHT) nanodiamonds have been investigated. The luminescence decay curves of color centers have been measured. Second order correlation functions were measured for nanodiamonds with sizes from 50 nm to 250 nm. Conclusions about the energy structure of color centers were made based on the correlation functions.

Metasurface” (MTS) denotes a surface constituted at microwave frequency by PCB or 3D printed elements small in terms of wavelengths that collectively exhibits equivalent homogeneous boundary conditions to any interacting electromagnetic fields. MTSs have had and are having a strong impact in Antenna applications. In the years 2000-2010 MTS for antennas were essentially uniform in space and realized by periodic printed elements. This was the first generation of MTS. In the present second generation (2010-2020) MTS for antennas are constructed in such a way to change boundary conditions in space to interact and shape the field launched by a feed. Today we are facing a transition to the third generation of MTS antennas, where MTSs change boundary conditions in space and time, opening new perspectives in 5G communications and beyond. In this presentation, MTS antennas of past and present generation are reviewed with ideas on possible future communication scenarios.

A CubeSat is a type of miniaturized satellite for space research [1], [2]. The basic unit for the CubeSat is a 1U cube with dimension 10 cm × 10 cm × 10 cm. CubeSats have a mass of no more than 1.33 kg per unit and often use commercial off-the-shelf (COTS) components for their electronics and structure. The CubeSats use solar cells to convert sunlight to electricity, which is then stored in rechargeable batteries that power the CubeSats. The CubeSats have a limited external surface area for solar cell assembly, and this area has to be effectively shared with other parts, such as antennas, optical sensors, camera lenses, propulsion systems, and access ports [3]. Accordingly, the solar antennas, which are integrated antennas with solar cells, represent one solution that allow more effective sharing of the surface areas of the CubeSats. The main challenge for solar antenna development is compatibility between the antenna and solar cell; i.e., the antennas should not block the functioning of the solar cells, and the effectiveness of the antennas should not be significantly reduced by the presence of the solar cells [4]–[6]. In this paper, two types of metasurface-based low-profile broadband solar antenna with circularly polarized radiation are presented for use in CubeSats. The first configuration is the solar antenna composed of a single-feed printed crossed-dipole antenna backed by a reflector, which is a 4 × 4 square lattice metasurface of solar cells mounted on a grounded dielectric substrate. The second configuration is the solar antenna composed of a slotted circular patch sandwiched between the 4 × 4 square lattice metasurface of solar cells and ground plane. These configurations produce broad operational impedance and axial ratio bandwidths and allow complete exposure of the solar cells to sunlight.

In recent years, there has been a boom in the development of the terahertz range. To be more precise to its long-wave part from 0.1 to 1.0 THz called sub THz waves. Sub-THz astronomy, radar and telecommunications have been widely developed last decade. The talk presents the main approaches to solving the main problems of sub-THz waves. Among them, a key place is occupied by the significant atmospheric absorption of these waves and the study of atmospheric absorption (microwave astroclimate), as well as the selection of adequate sites for the placement of radio telescopes and antennas for deep space communications, as well as radars effective for diagnosing of space debris using very high power gyrotrons and low noise receivers. Some of the results of astroclimate research, as well as specially developed equipment and methods, are presented. Another problem is associated with the practical lack of tools: antennas and receivers in this range. The development of these areas and the extensive experience of the team are presented. The key element of the author's developments is the creation of extremely high sensitive receivers of subHz waves, cooled to deep cryogenic temperatures including SubK levels, is presented in the talk.

Current communication systems demand high capacity and ubiquity, two conditions that are leading to a rapid evolution of wireless standards, which lead to broad operation bandwidths. The classical solutions of systems operating at microwaves are becoming unpractical due to the saturation of that part of the spectrum as well as the limited available bandwidth. In this context, millimeter-waves arise as the natural candidate for modern wireless communication systems with broad bandwidths and high throughput. Metasurfaces have revolutionized the research on electromagnetics in general, giving rise to compact and multifunctional devices in structures compatible with standard photolithography manufacturing techniques. Lenses are one of the devices with novel functionality that have found an unprecedented evolution using metasurfaces. These metasurface lenses, usually called metalenses, have led to improved resolution overcoming the diffraction limit and have been applied to antennas to enhance the gain. In this talk, I will summarize our latest advances of metalenses operating in the millimeter-wave and terahertz range. I will present a superoscillatory metalens with improved resolution and high efficiency operating near 300 GHz. In addition, I will present another metalens designed following the Pancharatnam-Berry or geometrical phase concept, consisting of a bi-layered structure and able to focus circularly polarized waves with high polarization purity. Both designs are numerically and numerically analyzed.

The range of short millimeter waves (SMMWs) covering the frequencies from 70 to 300 GHz attracts much interest in applied fields. On the scale of the electromagnetic spectrum such waves are distinguished by their unique features, which include: a relatively large penetration depth into various optically opaque materials; absence of ionizing effects vs. X-rays; attainability of mm spatial resolution acceptable for imagining of concealed targets; high sensitivity to metallic and water-containing media; lower diffraction divergence and high information capacity vs. microwaves. These features make SMMWs highly demanded in the tasks of security, non-destructive testing of materials, communications (e.g. 6G), high-resolution radars and automobile anti-collision systems, etc. In this talk, we present recent results of R&D activity focused on elaborating methods to effectively manipulate SMMWs using electrically tunable liquid crystals integrated with metamaterial structures. We consider unique nematic liquid crystals, which have been developed and optimized in our group for this spectral range and which are characterized by high optical anisotropy and low dielectric losses. The amplitude- and phase-changing devices are discussed together with some target applications. The latter include single pixel imaging and electronic beam steering.

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An indirect exciton (IX), also known as an interlayer exciton, is a bound pair of an electron and a hole confined in spatially separated layers. Due to their long lifetimes, IXs can cool below the temperature of quantum degeneracy. This provides an opportunity to experimentally study cold composite bosons. In this contribution, we overview our studies of cold IXs, presenting spontaneous coherence and Bose-Einstein condensation of IXs and phenomena observed in the IX condensate, including the spatially ordered exciton state, commensurability effect of exciton density wave, spin textures, Pancharatnam-Berry phase and long-range coherent spin transport. We present interference dislocations in condensate of IXs. Dislocations in interference patterns are observed in a variety of systems including atoms, polaritons, magnons, and optical systems. Interference dislocations have been associated with vortices. We present a new mechanism - the moiré effect, which leads to the appearance of dislocations in interference patterns. We show that this mechanism is the origin of interference dislocations in condensate of IXs. These interference dislocations are formed by IX condensate matter waves ballistically propagating over macroscopic distances. The ballistic exciton propagation over long times and over long distances is the evidence for exciton superfluidity.

In this work, we introduce the novel non-radiating state in a high-Q planar THz metamaterial. Pseudo-anapole arises when the trivial solution to the non-radiating state condition is met. When both toroidal and electric dipole responses are both suppressed at the resonance frequency, their far-field intensities tend to zero. The proposed effect is by definition different from anapole regime, which is conditioned by another solution to non-radiating state condition p=-ikT. A conceptual advantage of pseudo-anapole state is the arising possibility to study multipoles of other families and higher orders due to suppressed electric type radiation. The effect was confirmed both numerically and experimentally in terahertz frequency range.

The effectivity of Surface-Enhanced Raman Scattering (SERS) in 1D-periodic metal-dielectric (silver-silica) plasmonic lattices is calculated based on the optical reciprocity theorem and Fourier modal method. We analyze the physical nature of the resonances in SERS spectra. We show, for example, that vertical Fabry-Perot resonances in dielectric wires confined between metallic layers play a very important role in SERS enhancement. The numerical results are in good qualitative agreement with the previously obtained experimental data. The work is done in collaboration with Nikolay A. Gippius (Skolkovo Institute of Science and Technology), Igor V. Kukushkin (The Institute of Solid State Physics RAS), Sergey G. Tikhodeev (Lomonosov Moscow State University and Prokhorov General Physics Institute RAS), and Thomas Weiss (4th Physics Institute and SCoPE, University of Stuttgart and Institute for Physics, University of Graz).

Geometrical chirality is a universal phenomenon that is encountered on many different length scales ranging from geometrical shapes of various living organisms to protein and DNA molecules. Interaction of chiral matter with chiral light – that is, electromagnetic field possessing a certain handedness – results in the well-known effect of circular dichroism, which underlies numerous techniques of discriminating molecular enantiomers. Enhancing dichroic effects is typically achieved by interfacing chiral matter with various optical resonators. In this context it is important to understand how the eigenmodes of optical cavities relate to the field states with well-defined handedness. In this talk, I will present the model of a single-handedness chiral optical cavity supporting only an eigenmode of a given handedness without the presence of modes of other helicity. Resonant excitation of the cavity with light of appropriate handedness enables formation of a helical standing wave with a uniform chirality density, while the opposite handedness does not cause any resonant effects. Furthermore, only enantiomers of the matching handedness efficiently interact with such a chiral eigenmode, enabling the handedness-selective light-matter interaction strength, thus expanding the set of tools for investigations of chiral matter and opening the door towards studies of chiral electromagnetic vacuum states.

Chiral semiconductor metasurfaces are known to demonstrate a giant optical activity, highly efficient circularly polarized light emissivity and routing. In my talk I plan to focus on the properties of Fano resonances in chiral metasurfaces, responsible for these important properties. Two examples of photonic structures will be considered: a circularly polarized laser based on a planar semiconductor microcavity with chiral modulated upper mirror, and a chiral semiconductor bi-metasurface for vertical routing of spin-polarized quantum dots' emission.

The applications of modern optoelectronic devices have been extended, and they now provide practical means for seamless real-time monitoring of blood flow dynamics, by being integrated with flexible and stretchable wearable sensor platform technology. However, thermal management of these devices remains limited by undesired thermal energy originating from the heating of the light-emitting diode. Specifically, the surface temperature of the optoelectronic device becomes very high compared to that of the adjacent biological tissue, causing challenges in skin–optoelectronics integration and functional deterioration of the light source. Such behavior becomes more significant under the solar irradiation. In this study, we introduce the integration of radiative coolers on the top of biointegrated optoelectronic modules for releasing the heat from the devices. The radiative coolers have broadband solar reflection properties as well as far-infrared emission characteristics that effectively minimize heat generation from the solar power. Successful demonstration of cooling behavior with wearable electronic devices under solar irradiation represents a major step forward in the field of temperature-sensitive, flexible, wearable electronic/optoelectronic devices.

Single-walled carbon nanotubes (SWCNTs) are among the strongest candidates for the replacement of commonly used transparent and conductive films (TCFs) based on doped metal oxides, such as indium tin oxide. SWCNTs possess unique multifunctional nature, which is based on their outstanding combination of mechanical strength and flexibility, chemical stability, exceptional electrical conductivity and optical properties. However, to fully utilize these properties in modern transparent electrode applications, SWCNT-based TCFs have to demonstrate the optoelectronic performance at the level of high-end ITO-based TCFs. This has not been achieved for SWCNT films yet and as a result limit their practical usage. Using gold chloride as the most effective dopant for the SWCNTs, we improve their optoelectrical characteristics by optimizing the doping solvent and conditions. We examined various solvents to push the optoelectrical performance of the TFCs based on SWCNTs. As a result, we obtained the sheet resistance as low as 40 Ω/□ at the transmittance of 90% (at 550 nm) using 15 mM HAuCl4 solution. This optoelectrical performance is better than that of ITO on PET substrates and satisfy most of the requirements for modern applications and relatively stable without additional protection over two years storing under ambient conditions. We propose a few interesting novel methods for SWCNT doping: aerosol doping and dip-coating methods will be discussed. The effect of the presence of catalyst particles on the optoelectronic properties of the SWCNT films is also investigated. Also, we propose a novel approach to enhance optoelectronic performance of SWCNTs using ionic liquid. The method provides fine and reversible tuning of optoelectrical properties of SWCNT films over a wide range of parameters. Using imidazolium-based ionic liquid with a wide electrochemical window (BMIM-PF6), we achieved the film sheet resistance as low as 53 Ω/sq at the 90% transmittance, thereby shifting the SWCNT Fermi level up to 1.4 eV. We believe the results to promote collateral research of adjustable tuning of the electronic structure of carbon nanomaterials as promising components for future electronics, electrochromic devices, and ionotronics. Although carbon nanotubes have been already demonstrated to be a promising material for bolometric photodetectors, the sensitivity enhancement while maintaining the speed of operation remains a great challenge. Here, we present a holey carbon nanotube network, designed to improve the temperature coefficient of resistance for highly sensitive ultra-fast broadband bolometers. Treatment of carbon nanotube films with low frequency oxygen plasma allows fine tuning of electronic properties of the material. The temperature coefficient of resistance of our films is much greater than reported values for pristine carbon nanotubes, up to -2.8%/K at liquid nitrogen temperature. The bolometer prototypes made of the treated films demonstrate high sensitivity in a wide IR range, short response time, smooth spectral characteristics and low noise level. And finally, we develop a novel transparent p-type flexible electrode based on SWCNTs combined with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), molybdenum oxide and SWCNT fibers. We achieved a record equivalent sheet resistance of 17 Ω/sq with a transmittance of 90% at 550 nm and a high degree of flexibility. We demonstrate that our solar cells based on the proposed electrode and hydrogenated amorphous silicon (a-Si:H) yield an outstanding short-circuit current density of Jsc = 15.03 mA/cm2 and a record power conversion efficiency of PCE = 8.8% for SWCNTs/a-Si:H hybrid solar cells. This work was supported by the Russian Science Foundation (Project identifier: 17-19-01787) and RFBR (project number: 20-03-00804).

The technology of creating patterned flexible electrodes based on single-walled carbon nanotubes and polydimethylsiloxane was demonstrated in this paper. A series of experiments were carried out to study whether the percolation affects the conductivity of patterned SWCNT layers. It was found that in patterns with the linewidth above 1 µm and the cell size above 50 µm the random character of SWCNT networks may be neglected. The impact of bending on the grid conductivity was studied. We observed a very moderate increase of resistance below 5% under the strain up to 4 %, which is comparable with the previous results for continuous SWCNT layers and shows the improvement in comparison with the previous reports on patterned SWCNT layers.

Flexible optoelectronic applications and devices are in high demand in wearable electronics, touchscreens of foldable gadgets, light-emitting devices (LED) and bright screens, electronic papers, implanted sensors, etc. Nowadays, the most developed flexible devices are based on organic materials. However, III-V semiconductor materials have advantages over conventional organic compounds in terms of long-term stability, electroluminescence properties and quantum efficiency, especially in the blue and red spectral ranges. Nanowires owing to their high length-to-diameter aspect ratio and geometrical shape possess outstanding mechanical properties, their rod-like form also facilitates the light waveguiding and light directivity, which are very essential for efficient light-emitting device development. Modern III-V semiconductor technology allows bandgap engineering and waveguide properties tailoring. In this work we present the synthesis of GaP nanowires with direct bandgap GaPAs insertions and their processing for efficient LEDs operating in red spectral range and IR-visualizers. The arrays of GaP/GaPAs nanowires grown by molecular beam epitaxy on Si substrate were encapsulated into flexible optically transparent polymer matrix and released from the growth substrate. Such flexible and stretchable membranes can be used for efficient IR-to-visible light visualizers, the converted light of which can be detected by the naked eye. Applying the transparent conductive layers based on the net of single wall carbon nanotubes to the open ends of nanowires embedded into polymer matrix allows contacting of these nanostructures for electroluminescence. We have shown experimentally that such transparent flexible GaP/GaPAs nanowires-based membranes can emitted light in the red spectral range, which is very important for RGB applications considering already available blue and green LEDs based on III-nitrides nanowires. The proposed approach for nanowire processing to flexible membranes can be also applied for development of piezogenerators, solar cells or IR-photodetectors based on (In)GaN, GaAs and InAs nanowires, respectively. Thus, III-V and III-N nanowires with fascinating optoelectronic properties pave the way for future flexible applications.

Nonlinear harmonic generation in nanostructures is one of the key topics in nanophotonics, as it allows infrared-to-visible light conversion at the nanoscale. This work reports on the efficient third-harmonic generation in a free-standing Si nanowire array encapsulated into a polymer membrane. High nonlinearity of Si material χ_1111^(3)=2.45∙10^(-19) m^2/V^2 and light coupling with optical resonances in the nanowires yield a strong third-harmonic signal and efficient infrared (1200-2000 nm) to visible (400-666 nm) upconversion. The fabricated membranes demonstrate high flexibility and semitransparency, which makes them convenient to use as visualizers.

Here we report optical analysis of individual GaPN NWs and flexible polymer/GaPN NW composite membranes. Heterostructured GaPN/GaP NWs were grown on Si (111) using plasma-assisted molecular beam epitaxy. The NW arrays were encapsulated into a polydimethylsiloxane (PDMS) matrix using the novel G-coating method and then exfoliated from the Si substrate.

Atom-like color centers in solids are attractive for applications in quantum technologies because their spin states exhibit long coherence times and can be controlled by optical and microwave fields. Spin control by acoustic vibrations is advantageous over microwaves because the acoustic fields can be efficiently confined in a well-defined area, allowing selective addressing of the spatially separated spin qubits. Moreover, the nature of the spin-phonon interaction allows spin transitions, which are forbidden for microwave fields, providing a basis for advanced quantum control protocols. In this contribution, we report on acoustically driven spin resonances in silicon vacancy centers in SiC. Specifically, we use the dynamic strain of surface acoustic waves to selectively excite spin transitions with magnetic quantum number differences of ±1 and ±2 in the absence of external microwave fields. These optically detected spin-acoustic resonances (SARs) reveal a non-trivial dependence on the orientation of the static magnetic field, which is attributed to the intrinsic symmetry of the acoustic fields combined with the peculiar properties of the 3/2-spin system. Compared to the ground states, spin levels in the optically accessible excited states possess even stronger interaction with strain fields, thus giving rise to novel and, so far, largely unexploited physical phenomena. A remarkable example is the acoustically induced coherent spin trapping: if the acoustic driving field is tuned in such a way that the spin precesses around the same axis in the ground and excited states, the optically detected SAR quenches due to the trapping of the spin projection along the precession axis and manifests a Fano-like shape. Our findings provide new opportunities for the coherent control of spin qubits with dynamic strain fields that can lead towards the realization of future spin-acoustic quantum devices.

We report the influence of static mechanical deformation on the zero-field spin splitting of silicon vacancies in silicon carbide at room temperature. We use AlN/6H-SiC heterostructures deformed by growth conditions and monitor the stress distribution as a function of distance from the heterointerface with spatially resolved confocal Raman spectroscopy. The zero-field spin splitting of the V1/V3 and V2 centers in 6H-SiC, measured by optically detected magnetic resonance, reveals significant changes at the heterointerface compared to the bulk value. This approach allows unambiguous determination of the spin-deformation interaction constant, which is 0.75 GHz/strain for the V1/V3 centers and 0.5 GHz/strain for the V2 centers. Provided piezoelectricity of AlN, our results offer a strategy to realize fine tuning of spin transition energies in SiC by deformation.

High-resolution spectroscopic studies of LaAlO3 single crystal doped with holmium ions are reported. Polarized and unpolarized absorption and luminescence spectra were measured in the broad spectral range from 2000 to 23 000 cm 1 at temperatures of 4.5–5 K. Additional measurements were fulfilled using site-selective laser spectroscopy. Energies and symmetry properties of the corresponding wave functions of crystal-field levels of Ho3+ ions which substitute for La3+ ions in LaAlO3 at sites with the D3 symmetry were determined with high accuracy, and, on this basis, crystal-field calculations were performed. A thorough analysis of spectral line profiles with the fine doublet structure corresponding to singlet-doublet transitions in the trigonal crystal field was made, which showed the existence of the random deformation splitting phenomenon. The value of deformation splitting lies in the region 0.3–0.8 cm-1 that substantially exceeds the widths of the doublet hyperfine splitting. The observed line shapes were successfully modeled, assuming the interaction of the Ho3+ ions with random deformations of the crystal lattice induced by point defects and ferroelastic domain boundaries.

The efficient control of the electron spin state is one of the main priorities in the development of modern spintronics. In particular, the most valuable are those methods that do not require the use of external magnetic fields. Conventional semiconductor structures, in which the spin can be electrostatically controlled via the Rashba spin-orbit coupling, need substantially low temperatures, and also have limitations on the switching time of the electron spin, which forces both experimentalist and theoreticians to search for new promising materials that are less demanding in temperature conditions and having a faster response. Moreover, from a practical point of view, the possibility of controlling the spin by means of light in the optical range looks extremely attractive. It will allow creating devices of a qualitatively different level possessing faster memory manipulation. In this regard, the family of such two-dimensional materials as chromium dichalcogenides, which have a unique combination of optical-magnetic properties, is extremely promising. In particular, in this work it is shown that the combination of pronounced excitonic and magnetic responses observed in chromium iodide, allows switching magnetization using light of a certain polarization. This effect is explained by the coupling of the electronic subsystem magnetization with an effective magnetic field arising from nonresonant pump of bright excitons. From a technical side, to demonstrate this effect, we analyzed a certain phenomenological model based on coupled equations of the Gross-Pitaevskii type for the density of spin-polarized excitons with the Landau-Lifshitz equation for electronic subsystem magnetization. In particular, we have shown the dependence of the switching time on the pump intensity, as well as on the presence of an external magnetic field of different orientations.

We demonstrated theoretically that formation of the resonant scattering states in the two-dimensional (2D) electron system irradiated by a circularly polarized electromagnetic field leads to the emergence of localized magnetic moments. As a consequence, the corresponding Kondo resonances appear. For GaAs-based quantum wells and microwave fields, we estimate the Kondo temperature around 2.5 K, which can be detected in state-of-the-art measurements.

We consider time-dependent processes in the optically excited hybrid system formed by a quantum well (QW) coupled to a remote spin-split correlated bound state. The spin-dependent tunneling from the QW to the bound state results in the nonequilibrium electron spin polarization in the QW. The Coulomb correlations at the bound state enhance the spin polarization in the QW. We propose two mechanisms for ultrafast switching of the spin polarization in the QW. One of them is based on the laser pulse frequency tuning between the bound state spin sublevels. Another one is associated with remote spin-split bound states. A mechanism of ultrafast PL polarization switching in this case is based on tunnel barrier transparency modulation. Such modulation can be experimentally realized by applying a gate voltage to the semiconductor heterostructure. The proposed mechanism is based on the split-off state energy level position being sensitive to the transparency of the tunnel barrier. Mn-doped core/multishell nanoplatelets and hybrid bound state-semiconductor heterostructures are suggested as promising candidates to prove the predicted effect experimentally. The obtained results open the possibility to form fully polarized PL signal and is promising for applications in spintronics, in particular, for ultrafast polarization modulation in spin lasers.

Implanted devices provide the opportunity to monitor and treat medical conditions wherever and whenever they occur. While the miniaturization of electronics has enabled a wide range of sensors for measuring physiological and biological parameters, major technological challenges remain in the way that these devices can remotely communicate and be controlled from the external world. Although originating in theoretical explorations of quantum mechanics, PT symmetry has recently emerged as a valuable concept in photonics, acoustics, and electronics because of the growing recognition that it underlies many exotic phenomena in systems with gain and loss. In this talk, I will describe how concepts in parity-time (PT) symmetry can enable wireless sensing, powering, and actuation of wireless implants beyond the limits of current systems. Three wireless technologies based on PT symmetry will be discussed: (1) a sensing system locked to an exceptional point that enables remote readout of an implanted microsensor, (2) a power transfer system that exploits nonlinear PT symmetry for selective transfer, and (3) an actuation system that provides highly controllable manipulation of circuits without magnets. Taken together, these systems illustrate the potential of concepts in non-Hermitian physics to overcome current limitations in wireless systems, which may pave the way for the next generation of miniaturized medical devices.

Today's wireless power transfer (WPT) technologies exploit outdated electromagnetic field control methods proposed in the 20th century suffering from many serious shortcomings, including low efficiency, instability, and short-distance operation. The development of novel approaches to electromagnetic field manipulation has enabled many up-and-coming technologies holding great promises for advanced wireless power transfer. The examples include coherent perfect absorption, exceptional points (EPs) in non-Hermitian systems, non-radiating states and anapoles, advanced artificial materials, metastructures, and topological states. In my talk, I will present our recent results in coherently enhanced wireless power transfer. I will show that there is a possibility to improve the WPT efficiency by coherent excitation of the outcoupling waveguide by a backward propagating guided mode with a specific amplitude and phase. This additional wave creates a special interference picture in the system and result in increased amount of energy extracted to the waveguide from the free space. The results of experimental realization of this approach in free-space and over a metasurface will be provided.

The main challenge in near-field wireless power transfer systems is the increase of power transfer efficiency. It can be achieved by reducing ohmic or radiation losses of the resonators included in the system. In this paper, we propose and investigate numerically a non-radiating near-field wireless power transfer system based on transmitter and receiver implemented as dielectric disk resonators. The transmitter and receiver geometrical parameters are numerically optimized to operate at the frequency of non-radiating state of high refractive index dielectric resonators instead of magnetic dipole mode. Under the non-radiating state, we determine the frequency with almost zero radiation to the far-field. We numerically study the wireless power transfer efficiency as a function of operation distance between the transmitter and receiver and demonstrate that the higher efficiency compared to magnetic dipole mode can be achieved at non-radiating state for a fixed distance due to suppression of the radiation loss.

In this paper I will discuss near-field wireless power transfer (WPT) systems. I will mainly conside the systems implemented as one transmitter to charge many recievers. The main physical mechanisms for such systems design will be discussed. Several prototypes of WPT systems operating at 6.78 MHz will be demonstrated. Their advantages, functionality, drawbacks and limitations will be shown and discussed.

Metasurface, 2D analogue of metamaterials, has been widely used for controlling the propagating electromagnetic waves. In this talk, we will discuss several metasurface designs to efficiently generate desired magnetic fields that are required by WPT applications.