Publications
2024

(2024) Physical Review A. 109, 6, L061501. Abstract
We discuss a generalization of the nonHermitian skin effect to finitesize photonic structures with neither gain nor loss in the bulk and a purely real energy spectrum under periodic boundary conditions (PBCs). We show that despite being Hermitian in the bulk, such systems can still have significant portions of eigenmodes concentrated at the edges and that this edge concentration can be linked to the nontrivial pointgap topology of the sizedependent regularized PBC spectrum, accounting for the radiative losses due to photon emission through the edges. We focus on a particular example of an array of atoms chirally coupled to the waveguide, but our results are also applicable to other systems with losses through the edges.
2023

(2023) Physical Review A. 108, 3, 033705. Abstract
We theoretically studied the scattering of short twophoton pulses from a spatially separated array of twolevel atoms coupled to the waveguide. A general analytical expression for the scattered pulse has been obtained. The contributions of various singleeigenstate and doubleexcited eigenstates of the array have been analyzed. We also calculated how the time, during which the incident photons are stored in the array, depends on the array period and the number of atoms. The largest storage times correspond to the structures with the antiBragg period, equal to the quarter of the wavelength of light at the atom resonance frequency λ/4.

(2023) Physical Review A. 108, 3, 033707. Abstract
We consider theoretically the mechanisms to realize antibunching between photons scattered on an array of twolevel atoms in a general electromagnetic environment. Our goal is antibunching that persists for times much longer than the spontaneous emission lifetime of an individual atom. We identify two mechanisms for such persistent antibunching. The first one is based on subradiant states of the atomic array and the second one does not require any subradiant states. We provide two specific examples of array parameters with optimized antibunching, based on an array in a free space and an array coupled to a waveguide.

(2023) Physical Review A. 108, 2, 023707. Abstract
We study theoretically quantum eigenstates in an array of twolevel atoms coupled to the waveguide. We show that this system features doubleexcited states where the two excitations are localized at the opposite edges of the array. Such bound states of distant excitations result from the longranged photonmediated coupling in the waveguide setup, which mediates repulsion at larger distances. These results could be useful for the rapidly developing field of waveguide quantum electrodynamics, studying waveguidecoupled arrays of cold atoms or superconducting qubits.

(2023) Physical Review A. 108, 2, 023715. Abstract
We have developed a theory of parametric photon generation in the waveguides coupled to arrays of quantum emitters with temporally modulated resonance frequencies. Such generation can be interpreted as a dynamical Casimir effect. We demonstrate numerically and analytically how the emission directionality and photonphoton correlations can be controlled by the phases of the modulation. The emission spectrum is shown to be strongly dependent on the anharmonicity of the emitter potential. Single and doubleexcited state resonances have been identified in the emission spectrum.

(2023) Science (New York, N.Y.). 381, 6654, p. 193198 Abstract
Vortices are topologically nontrivial defects that generally originate from nonlinear field dynamics. Alloptical generation of photonic vorticesphase singularities of the electromagnetic fieldrequires sufficiently strong nonlinearity that is typically achieved in the classical optics regime. We report on the realization of quantum vortices of photons that result from a strong photonphoton interaction in a quantum nonlinear optical medium. The interaction causes faster phase accumulation for copropagating photons, producing a quantum vortexantivortex pair within the twophoton wave function. For three photons, the formation of vortex lines and a central vortex ring confirms the existence of a genuine threephoton interaction. The wave function topology, governed by two and threephoton bound states, imposes a conditional phase shift of π per photon, a potential resource for deterministic quantum logic operations.

(2023) Nature Communications. 14, 2998. Abstract
The ability to control the direction of scattered light is crucial to provide flexibility and scalability for a wide range of onchip applications, such as integrated photonics, quantum information processing, and nonlinear optics. Tunable directionality can be achieved by applying external magnetic fields that modify optical selection rules, by using nonlinear effects, or interactions with vibrations. However, these approaches are less suitable to control microwave photon propagation inside integrated superconducting quantum devices. Here, we demonstrate ondemand tunable directional scattering based on two periodically modulated transmon qubits coupled to a transmission line at a fixed distance. By changing the relative phase between the modulation tones, we realize unidirectional forward or backward photon scattering. Such an insitu switchable mirror represents a versatile tool for intra and interchip microwave photonic processors. In the future, a lattice of qubits can be used to realize topological circuits that exhibit strong nonreciprocity or chirality.

(2023) Photonics and Nanostructures  Fundamentals and Applications. 53, 101104. Abstract
Arrays of atoms coupled to photons propagating in a waveguide are now actively studied due to their prospects for generation and detection of quantum light. Quantum simulators based on waveguides with longrange couplings were also predicted to manifest unusual manybody quantum states. However, quantum tomography for large arrays with N ≳ 20 atoms remains elusive since it requires independent access to every atom. Here, we present a novel concept for analog emulation of such systems by unveiling an analogy between the setup of waveguide quantum electrodynamics and the classical problem of an electromagnetic wave propagating in a wire metamaterial. Experimentally measuring near electromagnetic fields, we emulate the twoparticle localization arising from polaritonpolariton interactions in the quantum problem. Our results demonstrate the potential of wire metamaterials to visualize quantum lightmatter coupling in a tabletop experiment and may be applied to emulate other exotic quantum effects, such as quantum chaos, and selfinduced topological states.

(2023) Fundamentals and Applications of Nonlinear Nanophotonics. p. 271287 Abstract
We present the fundamental concepts for enhancing photonpair generation through spontaneous parametric downconversion in nonlinear dielectric metasurfaces. We show that in metasurfaces with specially designed twodimensional (2D) or onedimensional (1D) nanopatterns, which support optical bound states in the continuum, the photon rate and spectral brightness can be enhanced by orders of magnitude when compared to unpatterned thin films. In the case of our 2D structure, the photon pairs are emitted close to the normal, while our 1D lattice can mediate emission in a broad angular pattern. We also identify the distinct physical mechanism of the enhancement associated with 2D hyperbolic transverse phase matching of the frequencies with nondegenerate photons. These results can provide a foundation for future advances in the development of ultraminiaturized quantum sources of entangled photons tailored for various applications.

(2023) Reviews of Modern Physics. 95, 1, 015002. Abstract
This review describes the emerging field of waveguide quantum electrodynamics concerned with the interaction of photons propagating in a waveguide with localized quantum emitters. The collective emitterphoton interactions can lead to both enhanced and suppressed coupling compared to the case of independent emitters. Here the focus is on guided photons and ordered emitter arrays, manifesting superradiant and subradiant states, bound photon states, and quantum correlations with promising quantum information applications. Recent groundbreaking experiments performed with different quantum platforms, including cold atoms, superconducting qubits, semiconductor quantum dots, and quantum solidstate defects, are highlighted. The review also provides a comprehensive introduction to theoretical techniques to study the interactions and dynamics of these emitters and the photons in the waveguide.

(2023) Physical Review B. 107, 4, 045131. Abstract
We present a theoretical study of the quantum states of two repelling spinless particles in a onedimensional tightbinding model with a simple periodic lattice and open boundary conditions. We demonstrate that, when the particles are not identical, their interaction drives nontrivial correlated twoparticle states, such as bound states and edge states, and induces interactioninduced flat bands. We show that the localization of the center of mass of the two particles enforces the localization of their relative motion, which means formation of the bound states. While the considered system is Hermitian, an insight into the bound states is provided by an approximate effective nonHermitian model for the relative motion that features the nonHermitian skin effect.

(2023) Physical Review Letters. 130, 2, 023601. Abstract
We develop a general theoretical framework to dynamically engineer quantum correlations and entanglement in the frequencycomb emission from an array of superconducting qubits in a waveguide, rigorously accounting for the temporal modulation of the qubit resonance frequencies. We demonstrate that when the resonance frequencies of the two qubits are periodically modulated with a π phase shift, it is possible to realize simultaneous bunching and antibunching in crosscorrelations as well as Bell states of the scattered photons from different sidebands. Our approach, based on the dynamical conversion between the quantum excitations with different parity symmetry, is quite universal. It can be used to control multiparticle correlations in generic dynamically modulated dissipative quantum systems.
2022

(2022) Applied Physics Letters. 121, 20, 204001. Abstract
The rapid progress in quantum information processing leads to a rising demand for devices to control the propagation of electromagnetic wave pulses and to ultimately realize universal and efficient quantum memory. While in recent years, significant progress has been made to realize slow light and quantum memories with atoms at optical frequencies, superconducting circuits in the microwave domain still lack such devices. Here, we demonstrate slowing down electromagnetic waves in a superconducting metamaterial composed of eight qubits coupled to a common waveguide, forming a waveguide quantum electrodynamics system. We analyze two complementary approaches, one relying on dressed states of the AutlerTownes splitting and the other based on a tailored dispersion profile using the qubits tunability. Our timeresolved experiments show reduced group velocities of down to a factor of about 1500 smaller than in vacuum. Depending on the method used, the speed of light can be controlled with an additional microwave tone or an effective qubit detuning. Our findings demonstrate high flexibility of superconducting circuits to realize custom band structures and open the door to microwave dispersion engineering in the quantum regime.

(2022) Physical Review A. 106, 4, 043723. Abstract
We study theoretically the competition between directional asymmetric coupling and disorder in a onedimensional array of quantum emitters chirally coupled through a waveguide mode. Our calculation reveals a highly nontrivial phase diagram for the eigenstates' spatial profile, nonmonotonously depending on the disorder and directionality strength. The increase of the coupling asymmetry drives the transition from Anderson localization in the bulk through delocalized states to chiralityinduced localization at the array edge. Counterintuitively, this transition is not smeared by strong disorder but becomes sharper instead. Our findings could be important for the rapidly developing field of waveguide quantum electrodynamics, where chiral interactions and disorder play crucial roles.

(2022) Physical Review A. 106, 3, L031702. Abstract
We study theoretically driven quantum dynamics in periodic arrays of twolevel qubits coupled to the waveguide. We demonstrate that strongly subradiant eigenstates of the master equation for the density matrix emerge under strong coherent driving for arrays with the antiBragg periods d=λ/4,3λ/4.... This happens even though are no such eigenstates at low driving powers and is directly manifested by longliving quantum correlations between the qubits.

(2022) Physical Review Research. 4, 1, 013058. Abstract
We study experimentally and theoretically the temperature dependence of transverse magnetic routing of light emission from hybrid plasmonicsemiconductor quantum well structures where the exciton emission from the quantum well is routed into surface plasmon polaritons propagating along a nearby semiconductormetal interface. In IIVI and IIIV directband semiconductors the magnitude of routing is governed by the circular polarization of exciton optical transitions, that is induced by a magnetic field. For structures comprising a (Cd,Mn)Te/(Cd,Mg)Te diluted magnetic semiconductor quantum well we observe a strong directionality of the emission up to 15% at low temperature of 20K and magnetic field of 485mT due to giant Zeeman splitting of holes mediated via the strong exchange interaction with Mn2+ ions. For increasing temperatures towards room temperature the magnetic susceptibility decreases and the directionality strongly drops to 4% at about 65 K. We also propose an alternative design based on a nonmagnetic (In,Ga)As/(In,Al)As quantum well structure, suitable for higher temperatures. According to our calculations, such structure can demonstrate emission directionality up to 5% for temperatures below 200 K and moderate magnetic fields of 1 T.

(2022) New Journal of Physics. 24, 3, 035006. Abstract
We reveal that strongly enhanced generation of photon pairs with narrow frequency spectra and sharp angular correlations can be realised through spontaneous parametric downconversion in metasurfaces. This is facilitated by creating metagratings through nanostructuring of nonlinear films of subwavelength thickness to support the extended bound state in the continuum resonances, associated with ultrahigh Qfactors, at the biphoton wavelengths across a wide range of emission angles. Such spectral features of photons can be beneficial for various applications, including quantum imaging. Our modelling demonstrates a pronounced enhancement, compared to unpatterned films, of the total photonpair generation rate normalized to the pump power reaching 1.75 kHz mW1, which is robust with respect to the angular bandwidth of the pump, supporting the feasibility of future experimental realisations.

(2022) Journal of Experimental and Theoretical Physics. 134, 2, p. 171182 Abstract
Abstract: We study theoretically interaction of opticallypumped excitons with acoustic waves in planar semiconductor nanostructures in the strongly nonlinear regime. We start with the multimode optomechanical lasing regime for optical pump frequency above the exciton resonance and demonstrate broadband chaoticlike lasing spectra. We also predict formation of propagating optomechanical domain walls driven by optomechanical nonlinearity for the optical pump below the exciton resonance. Stability conditions for the domain walls are examined analytically and are in agreement with direct numerical simulations. Our results apply to nonlinear sound propagation in the arrays of quantum wells or in the plane of Bragg semiconductor microcavities hosting excitonic polaritons.
2021

(2021) Physical Review A. 104, 6, 063719. Abstract
We study theoretically two vibrating quantum emitters trapped near a onedimensional waveguide and interacting with propagating photons. We demonstrate that in the regime of strong optomechanical interaction the coupling of light to multiple emitter vibrations can lead to the formation of spatially localized multiphonon modes, exhibiting paritytime (PT) symmetry breaking. These localized multiphonon states have been interpreted by analyzing the energy spectrum in the quasiclassical approximation.

(2021) npj Quantum Information. 7, 1, 34. Abstract
We reveal the emergence of quantum Hall phases, topological edge states, spectral Landau levels, and Hofstadter butterfly spectra in the twoparticle Hilbert space of an array of periodically spaced twolevel atoms coupled to a waveguide (waveguide quantum electrodynamics). While the topological edge states of photons require finetuned spatial or temporal modulations of the parameters to generate synthetic magnetic fields and the quantum Hall effect, here we demonstrate that a synthetic magnetic field can be selfinduced solely by atom–photon interactions. The fact that topological order can be selfinduced in what is arguably the simplest possible quantum structure shows the richness of these waveguide quantum electrodynamics systems. We believe that our findings will advance several research disciplines including quantum optics, manybody physics, and nonlinear topological photonics, and that it will set an important reference point for the future experiments on qubit arrays and quantum simulators.

(2021) npj Quantum Materials. 6, 1, 10. Abstract
Waveguide quantum electrodynamics offers a wide range of possibilities to effectively engineer interactions between artificial atoms via a onedimensional open waveguide. While these interactions have been experimentally studied in the few qubit limit, the collective properties of such systems for larger arrays of qubits in a metamaterial configuration has so far not been addressed. Here, we experimentally study a metamaterial made of eight superconducting transmon qubits with local frequency control coupled to the mode continuum of a waveguide. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super and subradiant states, as well as the emergence of a polaritonic bandgap. Making use of the qubits quantum nonlinearity, we demonstrate control over the latter by inducing a transparency window in the bandgap region of the ensemble. The circuit of this work extends experiments with one and two qubits toward a fullblown quantum metamaterial, thus paving the way for largescale applications in superconducting waveguide quantum electrodynamics.

(2021) 2021 Conference on Lasers and ElectroOptics (CLEO 2021). p. 2 Abstract
We study theoretically a periodic array of atoms coupled to a waveguide and demonstrate that atomphoton interactions lead to formation of selfinduced quantum Hall phases, Hofstadter butterfly and exotic localized threephoton states.

(2021) Physical Review B. 104, 20, 205309. Abstract
We study theoretically the spatial distribution of the polarizations in the array of resonant electromagnetic dipole emitters coupled to a onedimensional waveguide. The ratchet effect manifests itself in the spatial asymmetry of the distribution of the emitter occupations along the array under symmetrical pumping from both sides. The occupation asymmetry is driven by the periodic modulation in time of the emitter resonance frequencies. We find numerically and analytically the optimal conditions for maximal asymmetry. We also demonstrate that the ratchet effect can be enhanced due to the formation of topological electromagnetic edge states, enabled by the frequency modulation. Our results apply to classical structures with coupled resonators or arrays of semiconductor quantum wells as well as quantum setups with waveguidecoupled natural or artificial atoms.

(2021) Physical review letters. 127, 17, 173601. Abstract
We theoretically study subradiant states in an array of atoms coupled to photons propagating in a onedimensional waveguide focusing on the strongly interacting manybody regime with large excitation fill factor . We introduce a generalized manybody entropy of entanglement based on exact numerical diagonalization followed by a highorder singular value decomposition. This approach has allowed us to visualize and understand the structure of a manybody quantum state. We reveal the breakdown of fermionized subradiant states with increase of with the emergence of shortranged dimerized antiferromagnetic correlations at the critical point and the complete disappearance of subradiant states at .

(2021) Advanced Photonics. 3, 5, 055001. Abstract
We predict theoretically a regime of photonpair generation driven by the interplay of multiple bound states in the continuum resonances in nonlinear metasurfaces. This nondegenerate photonpair generation is derived from the hyperbolic topology of the transverse phase matching and can enable ordersofmagnitude enhancement of the photon rate and spectral brightness, as compared to the degenerate regime. We show through comprehensive simulations that the entanglement of the photon pairs can be tuned by varying the pump polarization, which can underpin future advances and applications of ultracompact quantum light sources.

(2021) Physical Review B. 104, 8, 085303. Abstract
We study theoretically optomechanical interactions in a semiconductor microcavity with an embedded quantum well under optical pumping by a Bessel beam, carrying a nonzero orbital momentum. Due to the transfer of orbital momentum from light to phonons, the microcavity can act as an acoustic circulator: It rotates the propagation direction of the incident phonon by a certain angle clockwise or anticlockwise. Due to the optomechanical heating and cooling effects, the circulator can also function as an acoustic laser emitting sound with nonzero angular momentum. Our calculations demonstrate the potential of semiconductor microcavities for compact integrable optomechanical devices.

(2021) Physical Review B. 104, 7, 075447. Abstract
We study theoretically optomechanical damping and amplification spectra for vibrations interacting with excitonic polaritons in a zerodimensional microcavity. We demonstrate that the spectra strongly depend on the ratio of the excitonphonon and the photonphonon coupling constants. The interference between these couplings enables a situation when optomechanical gain exists either only for a lower polaritonic resonance or only for an upper polaritonic resonance. Our results provide insight into the optomechanical interactions in various multimode systems, where several resonant oscillators, such as photons, plasmons, or excitons, are coupled to the same vibration mode.

(2021) Physical Review B. 103, 22, 224520. Abstract
Recent discoveries in topological physics hold promise for disorderrobust quantum systems and technologies. Topological states provide the crucial ingredient of such systems featuring increased robustness to disorder and imperfections. Here we use an array of superconducting qubits to engineer a onedimensional topologically nontrivial quantum metamaterial. By performing microwave spectroscopy of the fabricated array, we experimentally observe the spectrum of elementary excitations. We reveal not only the singlephoton topological states but also the bands of exotic bound photon pairs arising due to the inherent anharmonicity of qubits. Furthermore, we discuss the formation of the twophoton bound edgelocalized state and confirm the topological origin of our model demonstrating disorderrobust behavior of photonphoton correlation function for the topological edge state. Our work provides an experimental implementation of the topological model with attractive photonphoton interaction in a quantum metamaterial.

(2021) Physical Review B. 103, 18, L180410. Abstract
We demonstrate mechanisms of reciprocity breaking in nonlinear optics driven by the toroidal dipole moment which characterizes nontrivial spatial distributions of spins in solids. Using highresolution femtosecond spectroscopy at electronic resonances in the magnetoelectric antiferromagnet CuB2O4, we show that nonreciprocity reaches 100% for opposite magnetic fields due to the interference of nonlinear coherent sources of second harmonic generation originating from the toroidal dipole moment, applied magnetic field, and noncentrosymmetric crystal structure. The experimental results are corroborated by theoretical analysis based on the crystal and magnetic symmetry of CuB2O4. Our findings open degrees of freedom in nonlinear optics and pave the way for future nonreciprocal spinoptronic devices operating on the femtosecond timescale.

(2021) Physical review letters. 126, 20, 203602. Abstract
We study theoretically quantum states of a pair of photons interacting with a finite periodic array of twolevel atoms in a waveguide. Our calculation reveals twopolariton eigenstates that have a highly irregular wave function in real space. This indicates the Bethe ansatz breakdown and the onset of quantum chaos, in stark contrast to the conventional integrable problem of two interacting bosons in a box. We identify the longrange waveguidemediated coupling between the atoms as the key ingredient of chaos and nonintegrability. Our results provide new insights in the interplay between order, chaos, and localization in manybody quantum systems and can be tested in stateoftheart setups of waveguide quantum electrodynamics.

(2021) Physics of the Solid State. 63, 4, p. 621627 Abstract
Abstract: Propagation of acoustic waves in a quantumwell array, in which spatially modulated sound amplification and attenuation are implemented by optical excitation at a frequency close to the exciton resonance, has been studied theoretically. Sound dispersion near Bragg resonances corresponding to the modulation wave vector is calculated. Occurrence of “imaginary” stop bands, in which imaginary parts of the Bloch mode frequencies are split, is described. It is demonstrated that acoustic topological modes arise at the structure edge.

(2021) Physical Review A. 103, 4, 043718. Abstract
We study theoretically the secondorder correlation function g(2)(t) for photons transmitted through a periodic Braggspaced array of superconducting qubits, coupled to a waveguide. We demonstrate that photon bunching and antibunching persist much longer than both radiative and nonradiative lifetimes of a single qubit. Due to the Borrmann effect, that is a strongly nonMarkovian collective feature of lightqubit coupling inherent to the Bragg regime, the photonphoton correlations become immune to nonradiative dissipation. This persistence of quantum correlations opens new avenues for enhancing the performance of setups of waveguide quantum electrodynamics.

(2021) Physical Review B. 103, 8, 085425. Abstract
Optical spin control is the basis for ultrafast spintronics: circularly polarized light in combination with spinorbit coupling enables spin manipulation of electronic states in condensed matter. However, the conventional approach is limited to longitudinal spin initialization along one particular axis that is dictated by the direction of light propagation. Here, plasmonics opens new possibilities, allowing one to tailor light polarization at the nanoscale. We demonstrate ultrafast optical excitation of electron spin on femtosecond timescales via plasmontoexciton spin conversion. By time resolving the THz spin dynamics in a hybrid (Cd,Mn)Te quantumwell structure covered with a metallic grating, we unambiguously determine the orientation of the photoexcited electron spins which is locked to the propagation direction of the optically excited surface plasmon polaritons. Using the spin of the incident photons as an additional degree of freedom, one can adjust not only the longitudinal, but also the transverse electron spin components normal to the light propagation at will.

(2021) Physical Review A. 103, 2, 023720. Abstract
We provide the first classification of threephoton eigenstates in a finite periodic array of twolevel atoms coupled to a waveguide. We focus on the strongly subwavelength limit and show the hierarchical structure of the eigenstates in the complex plane. The main characteristic eigenstates are explored using entanglement entropy as a distinguishing feature. We show that the rich interplay of order, chaos and localization found in twophoton systems extends naturally to threephoton systems. There also exist interactioninduced localized states unique to threephoton systems such as bound trimers, corner states, and trimer edge states.
2020

(2020) Physical Review A. 102, 4, 043523. Abstract
We consider theoretically light scattering by a resonant layer that periodically moves in real space. At small frequencies of motion the scattered light spectrum reveals the frequency shift that is governed by the Doppler effect. At higher motion frequencies, the scattered light spectra acquire sidebands stemming from the Raman effect. We investigate the crossover between these two regimes and propose a realistic quantum well structure for its observation.

(2020) Physical Review B. 102, 14, 144438. Abstract
Strong coupling between two quanta of different excitations leads to the formation of a hybridized state that paves a way for exploiting new degrees of freedom to control phenomena with high efficiency and precision. A magnon polaron is the hybridized state of a phonon and a magnon, the elementary quanta of lattice vibrations and spin waves in a magnetically ordered material. A magnon polaron can be formed at the intersection of the magnon and phonon dispersions, where their frequencies coincide. The observation of magnon polarons in the time domain has remained extremely challenging because the weak interaction of magnons and phonons and their short lifetimes jeopardize the strong coupling required for the formation of a hybridized state. Here, we overcome these limitations by spatial matching of magnons and phonons in a metallic ferromagnet with a nanoscale periodic surface pattern. The spatial overlap of the selected phonon and magnon modes formed in the periodic ferromagnetic structure results in a high coupling strength which, in combination with their long lifetimes, allows us to find clear evidence of an optically excited magnon polaron. We show that the symmetries of the localized magnon and phonon states play a crucial role in the magnon polaron formation and its manifestation in the optically excited magnetic transients.

(2020) Physical review letters. 125, 18, 183601. Abstract
We develop a rigorous theoretical framework for interactioninduced phenomena in the waveguide quantum electrodynamics (QED) driven by mechanical oscillations of the qubits. Specifically, we predict that the simplest setup of two qubits, harmonically trapped over an optical waveguide, enables the ultrastrong coupling regime of the quantum optomechanical interaction. Moreover, the combination of the inherent open nature of the system and the strong optomechanical coupling leads to emerging paritytime (PT) symmetry, quite unexpected for a purely quantum system without artificially engineered gain and loss. The PT phase transition drives longliving subradiant states, observable in the stateoftheart waveguide QED setups.

(2020) ACS Photonics. 7, 9, p. 25472554 Abstract
Recent years have seen a tremendous interest to atomically thin membranes such as graphene or monolayers of transition metal dichalcogenides. Owing to their light mass and strong optical resonances, such membranes have become a promising platform for nanoscale resonant optomechanics. However, the considerations of the lightmembrane interaction have been mostly restricted to the wellknown light pressure and heating. Here, we theoretically predict a fundamentally different optomechanical effect that is specific for membranes. Namely, we demonstrate that illumination of optically resonant membranes by a plane electromagnetic wave directly affects their mechanical tension. The induced optomechanical tension is anisotropic and, depending on the spectral detuning from the resonance, can be both positive and negative. In the latter case, it can overcome the bending rigidity of the membrane leading to transition to the crumpled phase. Our fundamental findings apply from manipulation of biological cell membranes to controllable furling and unfurling of solar sails.

(2020) Physical Review B. 102, 12, 125307. Abstract
In onedimensional chains of trapped Rydberg excitons in cuprous oxide semiconductor the topological spin phase has been recently predicted [Phys. Rev. Lett. 123, 126801 (2019)PRLTAO0031900710.1103/PhysRevLett.123.126801]. This phase is characterized by the diluted antiferromagnetic order of pshell exciton angular momenta1 and the edge states behaving akin to spin1/2 fermions. Here we study the properties of the ground state in the finite chains and its fine structure resulting from the effective interaction of the edge spins. We demonstrate that 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. We calculate the distribution of the exciton angular momentum vs. trap number in the chain numerically and analytically based on the variational ansatz.

(2020) Physical Review Research. 2, 3, 033190. Abstract
We study topological properties of bound pairs of photons in spatially modulated qubit arrays (arrays of twolevel atoms) coupled to a waveguide. While bound pairs behave like Bloch waves, they are topologically nontrivial in the parameter space formed by the centerofmass momentum and the modulation phase, where the latter plays the role of a synthetic dimension. In a superlattice where each unit cell contains three twolevel atoms (qubits), we calculate the Chern numbers for the boundstate photon bands, which are found to be (1,2,1). For open boundary conditions, we find exotic topological boundpair edge states with radiative losses. Unlike the conventional case of the bulkedge correspondence, these novel edge modes not only exist in gaps separating the boundpair bands but they also may merge with and penetrate into the bands. By joining two structures with different spatial modulations, we find longlived interface states which may have applications in storage and quantum information processing.

(2020) Physical Review A. 101, 4, 043848. Abstract
We calculate theoretically the transverse magnetooptical Kerr effect (TMOKE) in the periodically patterned waveguide made from a diluted magnetic semiconductor. It is demonstrated that the TMOKE is resonantly enhanced when the incident wave is in resonance with the bound state in continuum, arising when the quality factor of the leaky waveguide mode increases due to farfield interference. Our results uncover the potential of alldielectric and semiconductor nanostructures for resonant magnetooptics.

(2020) Physical Review A. 101, 4, 043845. Abstract
We study theoretically the radiative lifetime of bound twoparticle excitations in a waveguide with an array of twolevel atoms, realizing a onedimensional Dickelike model. Recently, Zhang et al. have numerically found an unexpected sharp maximum of the bound pair lifetime when the array period d is equal to 1/12th of the light wavelength λ0 [Phys. Rev. Research 2, 013173 (2020)10.1103/PhysRevResearch.2.013173]. We uncover a rigorous transformation from the nonHermitian Hamiltonian with the longrange radiative coupling to the nearestneighbor coupling model with the radiative losses only at the edges. This naturally explains the puzzle of long lifetime: The effective mass of the bound photon pair also diverges for d=λ0/12, hampering an escape of photons through the edges. We also link the oscillations of the lifetime with the number of atoms to the nonmonotonous quasiflatband dispersion of the bound pair.

(2020) Physical review letters. 124, 9, 093604. Abstract
We predict the existence of a novel interactioninduced spatial localization in a periodic array of qubits coupled to a waveguide. This localization can be described as a quantum analogue of a selfinduced optical lattice between two indistinguishable photons, where one photon creates a standing wave that traps the other photon. The localization is caused by the interplay between onsite repulsion due to the photon blockade and the waveguidemediated longrange coupling between the qubits.
2019

(2019) Physical review letters. 123, 25, 253601. Abstract
We develop a rigorous theoretical approach for analyzing inelastic scattering of photon pairs in arrays of twolevel qubits embedded into a waveguide. Our analysis reveals a strong enhancement of the scattering when the energy of incoming photons resonates with the doubleexcited subradiant states. We identify the role of different doubleexcited states in the scattering, such as superradiant, subradiant, and twilight states, as a product of singleexcitation bright and subradiant states. Importantly, the Nexcitation subradiant states can be engineered only if the number of qubits exceeds 2N. Both the subradiant and twilight states can generate longlived photonphoton correlations, paving the way to storage and processing of quantum information.

(2019) Physical Review A. 100, 5, 053813. Abstract
We study theoretically an extended BoseHubbard model with the spatially modulated interaction strength, describing a onedimensional array of tunnelingcoupled nonlinear cavities. It is demonstrated that the spatial modulation of the nonlinearity induces bound twophoton edge states. The formation of these edge states has been understood analytically in terms of nonlinear selflocalization. Our results show that the number of excitations and the modulation period of the interaction affect the photonic quantum walks in the universal way and both promote the edge states.

(2019) Nature Photonics. 13, 10, p. 692696 Abstract
The topological phases of matter are characterized using the Berry phase, a geometrical phase associated with the energymomentum band structure. The quantization of the Berry phase and the associated wavefunction polarization manifest as remarkably robust physical observables, such as quantized Hall conductivity and disorderinsensitive photonic transport^{1–5}. Recently, a novel class of topological phases, called higherorder topological phases, were proposed by generalizing the fundamental relationship between the Berry phase and quantized polarization, from dipole to multipole moments^{6–8}. Here, we demonstrate photonic realization of the quantized quadrupole topological phase, using silicon photonics. In our twodimensional secondorder topological phase, we show that the quantization of the bulk quadrupole moment manifests as topologically robust zerodimensional corner states. We contrast these topological states against topologically trivial corner states in a system without bulk quadrupole moment, where we observe no robustness. Our photonic platform could enable the development of robust onchip classical and quantum optical devices with higherorder topological protection.

(2019) Physical review letters. 123, 12, 126801. Abstract
We theoretically study Rydberg excitons in onedimensional chains of traps in Cu2O coupled via the van der Waals interaction. The triplet of optically active pshell states acts as an effective spin 1, and the interactions between the excitons are strongly spin dependent. We predict that the system has the topological Haldane phase with the diluted antiferromagnetic order, longrange string correlations, and finite excitation gap. We also analyze the effect of the trap geometry and interactions anisotropy on the Rydberg exciton spin states and demonstrate that a rich spin phase diagram can be realized showing high tunability of the Rydberg exciton platform.

(2019) Physical Review B. 100, 7, 075418. Abstract
I study theoretically quadrupolar topological insulators under applied static electric field rotated along the crystal axis. I demonstrate that the energy spectrum of this structure is a WannierStark ladder that naturally visualizes the quantization of nested Wilson loops for the bulk bands. This enables a direct distinction between the topological phase, possessing localized corner states, and the trivial phase, lacking the corner states. The crossover between the topological and trivial cases takes place via the nonadiabatic regime. These results may find applications in the characterization of rapidly emerging higherorder topological phases of light and matter.

(2019) Physical Review B. 99, 7, 075425. Abstract
We develop a multipolar theory of secondharmonic generation (SHG) by dielectric nanoparticles made of noncentrosymmetric materials with bulk quadratic nonlinearity. We specifically analyze two regimes of optical excitation: illumination by a plane wave and singlemode excitation, when the laser pump drives the magnetic dipole mode only. Considering two classes of nonlinear crystalline solids (dielectric perovskite material and IIIV semiconductor), we apply a symmetry approach to derive selection rules for the multipolar composition of the nonlinear radiation. The developed description can be used for design of efficient nonlinear optical nanoantennas with reconfigurable radiation characteristics.

(2019) Nature Nanotechnology. 14, 2, p. 126130 Abstract
Topological photonics has emerged as a route to robust optical circuitry protected against disorder^{1,2} and now includes demonstrations such as topologically protected lasing^{3–5} and singlephoton transport^{6}. Recently, nonlinear optical topological structures have attracted special theoretical interest^{7–11}, as they enable tuning of topological properties by a change in the light intensity^{7,12} and can break optical reciprocity^{13–15} to realize full topological protection. However, so far, nonreciprocal topological states have only been realized using magnetooptical materials and macroscopic setups with external magnets^{4,16}, which is not feasible for nanoscale integration. Here we report the observation of a thirdharmonic signal from a topologically nontrivial zigzag array of dielectric nanoparticles and the demonstration of strong enhancement of the nonlinear photon generation at the edge states of the array. The signal enhancement is due to the interaction between the Mie resonances of silicon nanoparticles and the topological localization of the electric field at the edges. The system is also robust against various perturbations and structural defects. Moreover, we show that the interplay between topology, bianisotropy and nonlinearity makes parametric photon generation tunable and nonreciprocal. Our study brings nonlinear topological photonics concepts to the realm of nanoscience.

(2019) Nanophotonics. 8, 2, p. 287296 Abstract
Magnetooptical spectroscopy based on the transverse magnetooptical Kerr effect (TMOKE) is a sensitive method for investigating magneticallyordered media. Previous studies were limited to the weak coupling regime where the spectral width of optical transitions considerably exceeded the Zeeman splitting in magnetic field. Here, we investigate experimentally and theoretically the transverse Kerr effect in the vicinity of comparatively narrow optical resonances in confined quantum systems. For experimental demonstration we studied the groundstate exciton resonance in a (Cd,Mn)Te diluted magnetic semiconductor quantum well, for which the strong exchange interaction with magnetic ions leads to giant Zeeman splitting of exciton spin states. For low magnetic fields in the weak coupling regime, the Kerr effect magnitude grows linearly with increasing Zeeman splitting showing a dispersive Sshaped spectrum, which remains almost unchanged in this range. For large magnetic fields in the strong coupling regime, the magnitude saturates, whereas the spectrum becomes strongly modified by the appearance of two separate peaks. TMOKE is sensitive not only to the sample surface but can also be used to probe in detail the confined electronic states in buried nanostructures if their capping layer is sufficiently transparent.

(2019) Physical Review X. 9, 1, 011008. Abstract
Tunable directional scattering is of paramount importance for operation of antennas, routing of light, and design of topologically protected optical states. For visible light scattered on a nanoparticle, the directionality could be provided by the Kerker effect, exploiting the interference of electric and magnetic dipole emission patterns. However, magnetic optical resonances in small sub100nm particles are relativistically weak. Here, we predict inelastic scattering with the unexpectedly strong tunable directivity up to 5.25 driven by a trembling of a small particle without any magnetic resonance. The proposed optomechanical Kerker effect originates from the vibrationinduced multipole conversion. We also put forward an optomechanical spinHall effect, the inelastic polarizationdependent directional scattering. Our results uncover an intrinsically multipolar nature of the interaction between light and mechanical motion and apply to a variety of systems from cold atoms to twodimensional materials to superconducting qubits. An application for engineering of chiral optomechanical coupling and nonreciprocal transmission at nanoscale is proposed.

(2019) 2019 Conference on Lasers and ElectroOptics (CLEO). Abstract
We observe topologically nontrivial nonlinear edge states of light in zigzag arrays of silicon nanoparticles. We image the edge states via the thirdharmonic generation and demonstrate their robustness against disorder and structural perturbations.

(2019) Optica. 6, 11, p. 14161422 Abstract
Optical nanoantennas have shown a great capacity for efficient extraction of photons from the near to the far field, enabling directional emission from nanoscale singlephoton sources. However, their potential for the generation and extraction of multiphoton quantum states remains unexplored. Here we experimentally demonstrate the nanoscale generation of twophoton quantum states at telecommunication wavelengths based on spontaneous parametric downconversion in an optical nanoantenna. The antenna is a crystalline AlGaAs nanocylinder, possessing Mietype resonances at both the pump and the biphoton wavelengths, and when excited by a pump beam it generates photon pairs with a rate of 35 Hz. Normalized to the pump energy stored by the nanoantenna, this rate corresponds to 1.4 GHz/Wm, being 1 order of magnitude higher than conventional onchip or bulk photonpair sources. Our experiments open the way for multiplexing several antennas for coherent generation of multiphoton quantum states with complex spatialmode entanglement and applications in freespace quantum communications and sensing.
2018

(2018) Physical Review A. 98, 6, 063625. Abstract
We present a strategy based on twodimensional arrays of coupled linear optical resonators to investigate the twobody physics of interacting bosons in onedimensional lattices. In particular, we want to address the bound pairs in topologically nontrivial SuSchriefferHeeger arrays. Taking advantage of the drivendissipative nature of the resonators, we propose spectroscopic protocols to detect and tomographically characterize bulk doublon bands and doublon edge states from the spatially resolved transmission spectra, and to highlight Feshbach resonance effects in twobody collision processes. We discuss the experimental feasibility using stateoftheart devices, with a specific eye on arrays of semiconductor micropillar cavities.

(2018) Optics Letters. 43, 24, p. 59175920 Abstract
We theoretically study the dissipative Bose–Hubbard model describing the array of tunnelingcoupled cavities with nonconservative photon–photon interaction. The bound twophoton states are formed in this system either in the limited range of the centerofmass wave vectors or in the full Brillouin zone, depending on the strength of the dissipative interaction. Transition between these two regimes is manifested as an exceptional point in the complex energy spectrum. This improves fundamental understanding of the interplay of nonHermiticity and interactions in the quantum structures and can potentially be used for ondemand nonlinear light generation in photonic lattices.

(2018) Physical Review B. 98, 16, 165129. Abstract
We demonstrate that the paritytime (PT) symmetric interfaces formed between nonHermitian amplifying ("gainy") and lossy topological crystals exhibit PT phase transitions separating phases of lossless and decaying/amplifying topological edge transport. The spectrum of these interface states exhibits exceptional points (EPs) separating (i) a PT symmetric realvalued regime with an evenly distributed wave function in both gainy and lossy domains and (ii) a PT broken complexvalued regime, in which edge states asymmetrically localize in one of the domains. Despite its complexvalued character, the edge spectrum remains gapless and connects complexvalued bulk bands through the EPs. We find that the regimes exist when the real edge spectrum is embedded into the bulk continuum without mixing, indicating that the edge states are protected against leakage into the bulk by the PT symmetry. Two exemplary PT symmetric systems, exhibiting valley and Chern topological phases, respectively, are investigated and the connection with the corresponding Hermitian systems is established. Interestingly, despite the complex bulk spectrum of the Chern insulator, the bulkinterface correspondence principle still holds, as long as the topological gap remains open. The proposed systems are experimentally feasible in photonics, which is evidenced by our rigorous fullwave simulations of PT symmetric siliconbased photonic graphene.

(2018) Physical review letters. 121, 16, 163901. Abstract
Topological photonics has emerged recently as a smart approach for realizing robust optical circuitry, and the study of nonlinear effects is expected to open the door for tunability of photonic topological states. Here we realize experimentally nonlinearityinduced spectral tuning of electromagnetic topological edge states in arrays of coupled nonlinear resonators in the pumpprobe regime. When nonlinearity is weak, we observe that the frequencies of the resonators exhibit spectral shifts concentrated mainly at the edge mode and affecting only weakly the bulk modes. For a strong pumping, we describe several scenarios of the transformation of the edge states and their hybridization with bulk modes, and also predict a parametrically driven transition from topological stationary to unstable dynamic regimes.

(2018) Nature Physics. 14, 10, p. 10431048 Abstract
Magnetooptical phenomena such as the Faraday and Kerr effects play a central role in controlling the polarization and intensity of optical fields propagating through a medium. Intensity effects in which the direction of light emission depends on the orientation of the external magnetic field are of particular interest, as they can be harnessed for routing light. Effects known so far for accomplishing such routing all control light emission along the axis parallel to the magnetic field. Here we report a new class of emission phenomena where directionality is established perpendicular to the externally applied magnetic field for light sources located in the vicinity of a surface. As a proof of principle for this effect, which we call transverse magnetic routing of light emission, we demonstrate the routing of emission for excitons in a dilutedmagneticsemiconductor quantum well. In hybrid plasmonic semiconductor structures, we observe significantly enhanced directionality of up to 60%.

(2018) Nature Physics. 14, 10, p. 1067 Abstract
In the version of this Article originally published, the expression for P _{c} was missing a division slash; it should have read P _{c} = ±2d _{y} d _{z} /(d _{y}^{2} + d _{z}^{2} ) ≈ ±2/3Δ _{h,F} /Δ _{1h} . Also, affiliation 5 was missing ‘Institute of Physics’; it should have read ‘International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland’. These issues have now been corrected.

(2018) Physical Review A. 98, 1, 013827. Abstract
We study solitons of the twodimensional nonlinear Dirac equation with asymmetric cubic nonlinearity. We show that with the nonlinearity parameters specifically tuned, a high degree of localization of both spinor components is enabled on a ring of certain radius. Such ring Dirac soliton can be viewed as a selfinduced nonlinear domain wall and can be implemented in nonlinear photonic graphene lattice with Kerrlike nonlinearities. Our model could be instructive for understanding localization mechanisms in nonlinear topological systems.

(2018) Physical Review B. 98, 4, 045415. Abstract
We propose a onedimensional nonlinear system of coupled anharmonic oscillators that dynamically undergoes a topological transition switching from the disordered and topologically trivial phase to the nontrivial one due to the spontaneous symmetry breaking. The topological transition is accompanied by the formation of the topological interface state in the spectrum of linearized excitations of the equilibrium phase. Our findings thus highlight the potential of the nonlinear systems for hosting the topological phases and uncover a fundamental link between the spontaneoussymmetrybreaking mechanism and topological interface states.

(2018) Semiconductors. 52, 4, p. 447451 Abstract
Photoluminescence, optical reflectance and electroreflectance spectroscopies were employed to study an AlGaAs/GaAs multiplequantumwell based resonant Bragg structure, which was designed to match optical Bragg resonance with the excitonpolariton resonance at the second quantum state in the GaAs quantum wells. The structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semiinsulating substrate by molecular beam epitaxy. Broad and enhanced optical and electroreflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons manifesting an enhancement of the lightmatter interaction under doubleresonance conditions. By applying an alternating electric field, we revealed electroreflectance features related to the x(e2hh2) and x(e2hh1) excitons. The excitonic transition x(e2hh1), which is prohibited at zero electric field, was allowed by a DC bias due to brake of symmetry and increased overlap of the electron and hole wave functions caused by electric field.

(2018) Light: Science and Applications. 7, 1, 133. Abstract
Increasing temperature is known to quench the excitonic emission of bulk silicon, which is due to thermally induced dissociation of excitons. Here, we demonstrate that the effect of temperature on the excitonic emission is reversed for quantumconfined silicon nanocrystals. Using laserinduced heating of silicon nanocrystals embedded in SiO_{2}, we achieved a more than threefold (>300%) increase in the radiative (photon) emission rate. We theoretically modeled the observed enhancement in terms of the thermally stimulated effect, taking into account the massive phonon production under intense illumination. These results elucidate one more important advantage of silicon nanostructures, illustrating that their optical properties can be influenced by temperature. They also provide an important insight into the mechanisms of energy conversion and dissipation in ensembles of silicon nanocrystals in solid matrices. In practice, the radiative rate enhancement under strong continuous wave optical pumping is relevant for the possible application of silicon nanocrystals for spectral conversion layers in concentrator photovoltaics.

(2018) Nano Letters. 18, 1, p. 535539 Abstract
Achieving efficient localization of white light at the nanoscale is a major challenge due to the diffraction limit, and nanoscale emitters generating light with a broadband spectrum require complicated engineering. Here we suggest a simple, yet highly efficient, nanoscale whitelight source based on a hybrid Si/Au nanoparticle with ultrabroadband (1.33.4 eV) spectral characteristics. We incorporate this novel source into a scanningprobe microscope and observe broadband spectrum of photoluminescence that allows fast mapping of local optical response of advanced nanophotonic structures with submicron resolution, thus realizing ultrabroadband nearfield nanospectroscopy.

(2018) Light: Science and Applications. 7, 1, 17143. Abstract
Integrated photonics is a leading platform for quantum technologies including nonclassical state generation 1, 2, 3, 4, demonstration of quantum computational complexity 5 and secure quantum communications 6. As photonic circuits grow in complexity, full quantum tomography becomes impractical, and therefore an efficient method for their characterization 7, 8 is essential. Here we propose and demonstrate a fast, reliable method for reconstructing the twophoton state produced by an arbitrary quadratically nonlinear optical circuit. By establishing a rigorous correspondence between the generated quantum state and classical sumfrequency generation measurements from laser light, we overcome the limitations of previous approaches for lossy multimode devices 9, 10. We applied this protocol to a multichannel nonlinear waveguide network and measured a 99.28±0.31% fidelity between classical and quantum characterization. This technique enables fast and precise evaluation of nonlinear quantum photonic networks, a crucial step towards complex, largescale, device production.

(2018) Nonlinear Photonics, NP 2018. Abstract
We propose the concept of atommediated pairgeneration, using the bandgap evanescent modes of a nonlinear periodic waveguide, where spontaneous generation of one photon becomes conditional on the absorption of its pair by a 2level emitter.

(2018) CLEO. Abstract
Relying on the bandgap modes of a nonlinear periodic waveguide, we propose the concept of atommediated spontaneous parametric downconversion, where photonpairs are only generated with a single 2level emitter present, creating a heralded excitation mechanism.

(2018) 2018 Conference on Lasers and ElectroOptics. Abstract
We generate a thirdharmonic field from topological photonic edge states in zigzag arrays of silicon nanoparticles. The effect is unidirectional due to the interplay of nonlinearity and bianisotropic coupling between electric and magnetic Mie resonances.

(2018) Conference on Lasers and ElectroOptics. Abstract
Paritytime (PT) symmetric interfaces between amplifying and lossy crystals support dissipationless edge states exhibiting gapless spectra in complex band structure if exceptional points (EPs) of edge states exist, which is verified by rigorous fullwave simulations in PTsymmetric photonic graphene.
2017

(2017) Journal of Physical chemistry c. 121, 49, p. 2776627773 Abstract
We study light absorption by nearly monodisperse PbS nanocrystals grown in a glass matrix. The absorption spectra demonstrate a wellresolved structure at energies above the first absorption peak. The absorption cross sections are calculated with an empirical tightbinding model accounting for the quantum confinement, the band anisotropy, and valley splittings. Absorption spectra measured at 4 K quantitatively agree with the atomistic calculations. This allows us to unambiguously ascribe the muchdebated second absorption peak to the pp optical transition and directly measure the splitting of excited p states.

(2017) Optics Letters. 42, 22, p. 47244727 Abstract
We propose the concept of atommediated spontaneous parametric downconversion, in which photonpair generation can take place only in the presence of a single twolevel emitter, relying on the bandgap evanescent modes of a nonlinear periodic waveguide. Using a guided signal mode, an evanescent idler mode, and an atomlike emitter with the idler’s transition frequency embedded in the structure, we find a heralded excitation mechanism, in which the detection of a signal photon outside the structure heralds the excitation of the embedded emitter. We use a rigorous Green’s function quantization method to model this heralding mechanism in a 1D periodic waveguide and determine its robustness against losses.

(2017) Nature Photonics. 11, 9, p. 543554 Abstract
Rapid progress in photonics and nanotechnology brings many examples of resonant optical phenomena associated with the physics of Fano resonances, with applications in optical switching and sensing. For successful design of photonic devices, it is important to gain deep insight into different resonant phenomena and understand their connection. Here, we review a broad range of resonant electromagnetic effects by using two effective coupled oscillators, including the Fano resonance, electromagnetically induced transparency, Kerker and Borrmann effects, and paritytime symmetry breaking. We discuss how to introduce the Fano parameter for describing a transition between two seemingly different spectroscopic signatures associated with asymmetric Fano and symmetric Lorentzian shapes. We also review the recent results on Fano resonances in dielectric nanostructures and metasurfaces.

(2017) Physical Review B. 96, 8, 085310. Abstract
We use an empirical tightbinding approach to calculate electron and hole states in [111]grown PbSe nanowires. We show that the valleyorbit and spinorbit splittings are very sensitive to the atomic arrangement within the nanowire elementary cell and differ for [111] nanowires with microscopic D3d,C2h, and D3 symmetries. For the nanowire diameter below 4 nm the valleyorbit splittings become comparable with the confinement energies and the k·p method is inapplicable. Nanowires with the D3 point symmetry having no inversion center exhibit giant spin splitting E=αkz, linear in onedimensional wave vector kz, with the constant α up to 1eVÅ.

(2017) Physical Review A. 95, 5, 053866. Abstract
We predict the existence of interactiondriven edge states of bound twophoton quasiparticles in a dimer periodic array of nonlinear optical cavities. The energy spectrum of photon pairs is dramatically richer than in the noninteracting case or in a simple lattice, featuring collapse and revival of multiple edge and bulk modes as well as edge states in continuum. We link the edgestate existence to the twophoton quantum walk graph connectivity. Our results offer a route to control quantum entanglement and provide insights into the physics of manybody topological states.

(2017) Physical review letters. 118, 15, 156801. Abstract
We develop a rigorous theoretical framework to describe lightsound interaction in the laserpumped periodic multiplequantumwell structure accounting for hybrid phononpolariton excitations, termed phonoritons. We show that phonoritons exhibit the pumpinginduced synthetic magnetic field in the artificial "coordinateenergy" space that makes transmission of left and right going waves different. The sound transmission nonreciprocity allows one to use such phonoritonic crystals with realistic parameters as optically controlled nanoscale acoustic diodes.

(2017) Journal of Applied Physics. 121, 10, 103101. Abstract
An AlGaAs/GaAs multiplequantumwell based resonant Bragg structure was designed to match the optical Bragg resonance with the excitonpolariton resonance at the second quantum state in the GaAs quantum wells. The sample structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semiinsulating GaAs substrate by molecular beam epitaxy. Angle and temperaturedependent photoluminescence, optical reflectance, and electroreflectance spectroscopies were employed to study the resonant optical properties of the Bragg structure. Broad and enhanced optical and electroreflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons, manifesting a strong lightmatter interaction. From the electrooptical experiments, we found the electroreflectance features related to the transitions of x(e2hh2) and x(e2hh1) excitons. The excitonic transition x(e2hh1), which is prohibited at zero electric field, was allowed by a DC bias due to the brake of symmetry and increased overlap of the electron and hole wave functions caused by the electric field. By tuning the Bragg resonance frequency, we have observed the electroreflectance feature related to the second quantum state up to room temperature, which evidences a robust lightmatter interaction in the resonant Bragg structure.

(2017) Physical Review A. 95, 3, 033831. Abstract
We study theoretically twophoton states in a periodic array of coupled cavities with both onsite and nonlocal Kerrtype nonlinearities. In the absence of nonlinearity the structure is topologically trivial and possesses no edge states. The interplay of two nonlinear interaction mechanisms described by the extended Hubbard model facilitates the formation of edge states of bound photon pairs. Numerical and exact analytical results for the twophoton wave functions are presented. Our findings thus shed light onto the edge states of composite particles and their localization properties.

(2017) Small. 13, 11, 1603190. Abstract
Recently introduced field of topological photonics aims to explore the concepts of topological insulators for novel phenomena in optics. Here polymeric chains of subwavelength silicon nanodisks are studied and it is demonstrated that these chains can support two types of topological edge modes based on magnetic and electric Mie resonances, and their topological properties are fully dictated by the spatial arrangement of the nanoparticles in the chain. It is observed experimentally and described how theoretically topological phase transitions at the nanoscale define a change from trivial to nontrivial topological states when the edge mode is excited.
2016

(2016) Physical review letters. 117, 22, 224302. Abstract
We demonstrate that the paritytime symmetry for sound is realized in laserpumped multiplequantumwell structures. Breaking of the paritytime symmetry for the phonons with wave vectors corresponding to the Bragg condition makes the structure a highly selective acoustic wave amplifier. Singlemode distributed feedback phonon lasing is predicted for structures with realistic parameters.

(2016) Physical review letters. 117, 12, 123901. Abstract
We develop a general theoretical framework of integrated paired photonplasmon generation through spontaneous wave mixing in nonlinear plasmonic and metamaterial nanostructures, rigorously accounting for material dispersion and losses in the quantum regime through the electromagnetic Green function. We identify photonplasmon correlations in layered metaldielectric structures with 70% internal heralding quantum efficiency and reveal a novel mechanism of broadband generation enhancement due to topological transition in hyperbolic metamaterials.

(2016) Journal of Physical Chemistry C. 120, 33, p. 1890118908 Abstract
We present a theoretical study of Gecore/Sishell nanocrystals in a wide bandgap matrix and compare the results with experimental data obtained from the samples prepared by cosputtering. The empirical tightbinding technique allows us to account for the electronic structure under strain on the atomistic level. We find that a Si shell as thick as one monolayer is enough to reduce the radiative recombination rate as a result of valley LX crossover. Thin Si shells lead to a dramatic reduction of the optical bandgap from the visible to the nearinfrared range, which is promising for photovoltaics and photodetector applications. Our detailed analysis of the structure of the confined electron and hole states in real and reciprocal spaces indicates that the typeII heterostructure is not yet achieved for Si shells with thicknesses below 0.8 nm, despite some earlier theoretical predictions. The energy levels of holes are affected by the Si shell more than the electron states, even though holes are completely confined to the Ge core. This occurs due to a strong influence of strain on the band offsets.

(2016) Laser and Photonics Reviews. 10, 4, p. 656664 Abstract
Photonic structures offer unique opportunities for controlling lightmatter interaction, including the photonic spin Hall effect associated with the transverse spindependent displacement of a light beam that propagates in specially designed optical media. However, due to small spinorbit coupling, the photonic spin Hall effect is usually weak at the nanoscale. Here we suggest theoretically and demonstrate experimentally, in both optics and microwave experiments, the photonic spin Hall effect enhanced by topologically protected edge states in subwavelength arrays of resonant dielectric particles. Based on direct nearfield measurements, we observe the selective excitation of the topological edge states controlled by the handedness of the incident light. Additionally, we reveal the main requirements to the symmetry of photonic structures to achieve the topologyenhanced spin Hall effect, and also analyse the robustness of the photonic edge states against the longrange coupling. (Figure presented.) .

Quasicrystalline Photonic Structures: Between Order and Disorder(2016) Optical Properties of Photonic Structures. p. 131150 Abstract

(2016) Advanced Materials. 28, 9, p. 18321838 Abstract
It is revealed that the unique properties of ultrathin metasurface resonators can improve magnetic resonance imaging dramatically. A metasurface formed when an array of metallic wires is placed inside a scanner under the studied object and a substantial enhancement of the radiofrequency magnetic field is achieved by means of subwavelength manipulation with the metasurface, also allowing improved image resolution.

(2016) Physical Review A. 93, 3, 033856. Abstract
The photon blockade is a hallmark of quantum light transport through a single twolevel system that can accommodate only one photon. Here, we theoretically show that twophoton transmission can be suppressed even for a system of a large number of quantum dots in a cavity when the biexciton nonlinearity is taken into account. We reveal the nonmonotonous dependence of the secondorder correlation function of the transmitted photons on the biexciton binding energy. The blockade is realized by proper tuning of the biexciton resonance that controls the collective superradiant modes.

(2016) 2016 Conference on Lasers and ElectroOptics. Abstract
We present the realization of an inhomogeneously poled nonlinear waveguide array for the generation of photon pairs with integrated pump filtering. The biphoton wavefunction produced from the device is characterized using reversed sumfrequency generation measurements.

(2016) Laser and Photonics Reviews. 10, 1, p. 137146 Abstract
We present a general theory of circular dichroism in planar chiral nanostructures with rotational symmetry. It is demonstrated, analytically, that the handedness of the incident field's polarization can control whether a nanostructure induces either absorption or scattering losses, even when the total optical loss (extinction) is polarizationindependent. We show that this effect is a consequence of modal interference so that strong circular dichroism in absorption and scattering can be engineered by combining Fano resonances with planar chiral nanoparticle clusters. The energy imparted by circularly polarized light on chiral matter is known to depend on the handedness of light; an effect known as a circular dichroism. This study reveals that an analogous effect can be realized in twodimensional, planar chiral, nanostructures through a form of circular dichroism in farfield radiation and nearfield material absorption that originates from Fanolike modal interference.

(2016) Journal of Experimental and Theoretical Physics. 122, 3, p. 531538 Abstract
We theoretically study nonradiative and radiative energy transfer between two localized quantum emitters, a donor (initially excited) and an acceptor (receiving the excitation). The rates of nonradiative and radiative processes are calculated depending on the spatial and spectral separation between the donor and acceptor states and for different donor and acceptor lifetimes for typical parameters of semiconductor quantum dots. We find that the donor lifetime can be significantly modified only due to the nonradiative Förster energy transfer process at donor–acceptor separations of approximately 10 nm (depending on the acceptor radiative lifetime) and for the energy detuning not larger than 1–2 meV. The efficiency of the nonradiative Förster energy transfer process under these conditions is close to unity and decreases rapidly with an increase in the donor–acceptor distance or energy detuning. At large donor–acceptor separations greater than 40 nm, the radiative corrections to the donor lifetime are comparable with nonradiative ones but are relatively weak.
2015

(2015) Physical review letters. 115, 26, 267402. Abstract
Polaritonmediated lightsound interaction is investigated through resonant Brillouin scattering experiments in GaAs/AlAs multiplequantum wells. Photoelastic coupling enhancement at excitonpolariton resonance reaches 105 at 30 K as compared to a typical bulk solid room temperature transparency value. When applied to GaAs based cavity optomechanical nanodevices, this result opens the path to huge displacement sensitivities and to ultrastrong coupling regimes in cavity optomechanics with couplings g0 in the range of 100 GHz.

(2015) Physical Review B  Condensed Matter and Materials Physics. 92, 21, 214436. Abstract
We study the optical properties of arrays of ultrathin cobalt nanowires by means of the Brillouin scattering of light on magnons. We employ the Stokes/antiStokes scattering asymmetry to probe the circular polarization of a local electric field induced inside nanowires by linearly polarized light waves. We observe the anomalous polarization conversion of the opposite sign than that in a bulk medium or thick nanowires with a great enhancement of the degree of circular polarization attributed to the unconventional refraction in a nanowire medium. A rigorous simulation of the electric field polarization as a function of the wire diameter and spacing reveals the reversed polarization for a thin sparse wire array, in full quantitative agreement with experimental results.

(2015) Physical Review B  Condensed Matter and Materials Physics. 92, 15, 155418. Abstract
We present a theory of Förster energy transfer between arrays of molecules lying on the planar metallic mirror. First, we calculate the complex band structure of the collective Bloch modes of the lightcoupled donor molecules. Next, we determine the effective rate of the energy transfer from the donors to the acceptors and reveal its strong modification by the mirror. The rate can be either suppressed or enhanced depending on the relative positions between the acceptor and donor arrays. The strong modification of the transfer rate is a collective effect, mediated by the coupling between the donors; it is absent in the singledonor model.

(2015) Journal of Physical Chemistry C. 119, 33, p. 1956519570 Abstract
Energy exchange between closely packed semiconductor quantum dots allows for longrange transfer of electronic energy and enables new functionalities of nanostructured materials with a huge application potential in photonics, optoelectronics, and photovoltaics. This is illustrated by impressive advances of quantumdot solids based on nanocrystals (NCs) of direct bandgap materials, where this effect has been firmly established. Regretfully, the (resonant) energy transfer in closepacked ensembles of NCs remains elusive for siliconthe main material for electronic and photovoltaic industries. This is the subject of the present study in which we conclusively demonstrate this process taking place in dense dispersions of Si NCs in an SiO_{2} matrix. Using samples with different NC configurations, we can directly determine the wavelength dependent energy transfer rate and show that it (i) can be modulated by material parameters, and (ii) decreases with the NCs size, and thus being consistent with the energy flow proceeding from smaller to larger NCs. This result opens the way to new applications of Si NCs, requiring energy transport and extraction. In particular, it forms a fundamental step toward development of an excitonic allSi solar cell, operating in some analogy to polymer devices.

(2015) Scientific Reports. 5, 12956. Abstract
The Purcell effect is defined as a modification of the spontaneous emission rate of a quantum emitter at the presence of a resonant cavity. However, a change of the emission rate of an emitter caused by an environment has a classical counterpart. Any small antenna tuned to a resonance can be described as an oscillator with radiative losses, and the effect of the environment on its radiation can be modeled and measured in terms of the antenna radiation resistance, similar to a quantum emitter. We exploit this analogue behavior to develop a general approach for calculating the Purcell factors of different systems and various frequency ranges including both electric and magnetic Purcell factors. Our approach is illustrated by a general equivalent scheme, and it allows resenting the Purcell factor through the continuous radiation of a small antenna at the presence of an electromagnetic environment.

(2015) Nanoscale. 7, 28, p. 1190411908 Abstract
We report on the first experimental observation of topological edge states in zigzag chains of plasmonic nanodisks. We demonstrate that such edge states can be selectively excited with the linear polarization of the incident light, and visualize them directly by nearfield scanning optical microscopy. Our work provides experimental verification of a novel paradigm for manipulating light at the nanoscale in topologically nontrivial structures.

Control of Förster energy transfer in the vicinity of metallic surfaces and hyperbolic metamaterials(2015) Faraday Discussions. 178, p. 395412 Abstract
Optical cavities, plasmonic structures, photonic band crystals and interfaces, as well as, generally speaking, any photonic media with homogeneous or spatially inhomogeneous dielectric permittivity (including metamaterials) have local densities of photonic states, which are different from that in vacuum. These modified density of states environments are known to control both the rate and the angular distribution of spontaneous emission. In the present study, we question whether the proximity to metallic and metamaterial surfaces can affect other physical phenomena of fundamental and practical importance. We show that the same substrates and the same nonlocal dielectric environments that boost spontaneous emission, also inhibit Förster energy transfer between donor and acceptor molecules doped into a thin polymeric film. This finding correlates with the fact that in dielectric media, the rate of spontaneous emission is proportional to the index of refraction n, while the rate of the donoracceptor energy transfer (in solid solutions with a random distribution of acceptors) is proportional to n^{1.5}. This heuristic correspondence suggests that other classical and quantum phenomena, which in regular dielectric media depend on n, can also be controlled with customtailored metamaterials, plasmonic structures, and cavities.

(2015) Photonics. 2, 2, p. 745757 Abstract
We reveal that asymmetric plasmonic nanostructures can exhibit significantly different absorption and scattering properties for light that propagates in opposite directions, despite the conservation of total extinction. We analytically demonstrate that this is a consequence of nonorthogonality of eigenmodes of the system. This results in the necessity for modal interference with potential enhancement via Fano resonances. Based on our theory, we propose a stacked nanocross design whose optical response exhibits an abrupt change between absorption and scattering crosssections for plane waves propagating in opposite directions. This work thereby proposes the use of Fano resonances to employ nanostructures for measuring and distinguishing optical signals coming from opposite directions.

(2015) Physical review letters. 114, 18, 185501. Abstract
We study the scattering of polaritons by free electrons in hyperbolic photonic media and demonstrate that the unconventional dispersion and high local density of states of electromagnetic modes in composite media with hyperbolic dispersion can lead to a giant Comptonlike shift and dramatic enhancement of the scattering cross section. We develop a universal approach to study multiphoton processes in nanostructured media and derive the intensity spectrum of the scattered radiation for realistic metamaterial structures.

(2015) Physical Review B  Condensed Matter and Materials Physics. 91, 20, 205126. Abstract
We theoretically demonstrate the strong Purcell effect in εnearzero ultraanisotropic uniaxial metamaterials with an elliptic isofrequency surface. Contrary to the hyperbolic metamaterials, the effect does not rely on the diverging density of states and evanescent waves. As a result, both the radiative decay rate and the farfield emission power are enhanced. The effect can be realized in the periodic layered metaldielectric nanostructures with a complex unit cell containing two different metallic layers.

(2015) Physical Review B  Condensed Matter and Materials Physics. 91, 19, 195401. Abstract
Optical metasurfaces have become a new paradigm for creating flat optical devices. While being typically an order of magnitude thinner than the wavelength of light, metasurfaces allow control of the phase of propagating light waves across the full 2π range and therefore enable the realization of optical elements such as lenses, waveplates, and beam converters. Currently one of the limiting factors of functional metasurfaces is their small range of operational angles. Here we demonstrate both theoretically and experimentally that the angular range can be broadened by increasing the rotational symmetry of metasurfaces. We develop an analytical model based on the discrete dipole approximation that quantitatively describes the response of metasurfaces under oblique excitation. It shows that the effective optical symmetry is doubled for structures with odd rotational symmetry, increasing the angular range correspondingly. We apply and experimentally verify our model for metasurfaces consisting of identical metaatoms, arranged into square lattices, hexagonal lattices, and on the vertices of a Penrose tiling. The results demonstrate the increasing angular performance with increasing rotational symmetry.

(2015) Physical Review A  Atomic, Molecular, and Optical Physics. 91, 4, 043830. Abstract
We propose a method of measuring topological invariants of a photonic crystal through phase spectroscopy. We show how the Chern numbers can be deduced from the winding numbers of the reflection coefficient phase. An explicit proof of the existence of edge states in a system with a nonzero reflection phase winding number is given. The method is illustrated for one and twodimensional photonic crystals of nontrivial topology.

(2015) Physical review letters. 114, 12, 123901. Abstract
We suggest a novel type of photonic topological edge states in zigzag arrays of dielectric nanoparticles based on optically induced magnetic Mie resonances. We verify our general concept by the proofofprinciple microwave experiments with dielectric spherical particles, and demonstrate, experimentally, the ability to control the subwavelength topologically protected electromagnetic edge modes by changing the polarization of the incident wave.

(2015) Proceedings of the National Academy of Sciences of the United States of America. 112, 13, p. E1516E1519 Abstract
Bosons with finite lifetime exhibit condensation and lasing when their influx exceeds the lasing threshold determined by the dissipative losses. In general, different oneparticle states decay differently, and the bosons are usually assumed to condense in the state with the longest lifetime. Interaction between the bosons partially neglected by such an assumption can smear the lasing threshold into a threshold domaina stable lasing manybody state exists within certain intervals of the bosonic influxes. This recently described weak lasing regime is formed by the spontaneously symmetry breaking and phaselocking selforganization of bosonic modes, which results in an essentially manybody state with a stable balance between gains and losses. Here we report, to our knowledge, the first observation of the weak lasing phase in a onedimensional condensate of excitonpolaritons subject to a periodic potential. Real and reciprocal space photoluminescence images demonstrate that the spatial period of the condensate is twice as large as the period of the underlying periodic potential. These experiments are realized at room temperature in a ZnO microwire deposited on a silicon grating. The period doubling takes place at a critical pumping power, whereas at a lower power polariton emission images have the same periodicity as the grating.

(2015) Journal of Optics (United Kingdom). 17, 3, 035102. Abstract
We present a theory of the local field corrections to the spontaneous emission rate for the array of silicon nanocrystals in silicon dioxide. An analytical result for the Purcell factor is obtained. We demonstrate that the localfield corrections are sensitive to the volume fill factor of the nanocrystals in the sample and are suppressed for large values of the fill factor. The localfield corrections and the photonic density of states are shown to be described by two different effective permittivities: the harmonic mean between the nanocrystal and the matrix permittivities and the MaxwellGarnett permittivity.
2014

(2014) Physical Review B  Condensed Matter and Materials Physics. 90, 24, 245439. Abstract
We propose a theoretical concept of switching between direct and indirect band gap character in silicon quantum dots (SiQDs) by the use of surface potential induced by the ligands or environment in which SiQDs are immersed  both cases are studied. Theoretical simulations show that the density of states of confined electrons in both real and k space can be dramatically altered by engineering the local electrostatic field. Especially interesting is modification of the lowest excited states, which appear in the Γ valley for electronegative field that "pulls" electrons towards the SiQD surface. Opposite sign of the field does not have such effect at all. Hence we conclude a general trend of promotion of directlike radiative transitions by electronegative capping/environment. The rates are enhanced by more than two orders of magnitude compared to "normal" SiQDs, which can be as high as the values characteristic for direct band gap semiconductors. This model is in agreement with observed experimental properties of SiQDs with covalently bonded electronegative ligands.

(2014) Physical Review A  Atomic, Molecular, and Optical Physics. 90, 2, 023854. Abstract
We present a theoretical study of the discrete Green's function for the twodimensional metamaterial, realized as a transmission line array. We demonstrate that the Green's function possesses distinct ripples when the isofrequency contour is of hyperbolic shape. This effect is a characteristic nonlocal feature of the hyperbolic regime and is beyond the effective medium approximation.

(2014) Physical Review B  Condensed Matter and Materials Physics. 90, 3, 035106. Abstract
We consider a torque acting on an electric dipole placed in anisotropic uniaxial metamaterial. The metamaterial is modeled as a cubic lattice of uniaxial polarizable particles. The torque arises from the response of the anisotropic structure polarized by the field of the test dipole. We calculate the selfinduced torque taking into account the effects of frequency and spatial dispersion and also the effect of losses. We demonstrate that the maximal absolute values of the torque are achieved in the transition region between elliptic and hyperbolic dispersion regimes of the metamaterial.

(2014) Physical Review B  Condensed Matter and Materials Physics. 89, 23, 235313. Abstract
We present theoretical and experimental study of resonant Brillouin scattering of excitonic polaritons in onedimensional multiplequantumwell structure. We obtain general analytical results for the scattering light spectra, valid for arbitrary quantumwell arrangement. Application of our theory to the specific case of shortperiod superlattice shows a perfect quantitative agreement with experimental results for the height, width, and position of the Brillouin scattering peaks and allows us to determine the energy, radiative, and nonradiative decay rates of quantumwell excitons. We reveal the signatures of excitonic polariton formation in the scattering spectra and show that the spectral width and height are strongly sensitive to the number of wells in the sample.

(2014) Applied Physics Letters. 104, 16, 161105. Abstract
We present an experimental study of the magnetic Purcell effect in finite arrays of the wire metamaterial. By directly measuring the spatialfrequency map of the Purcell factor, we explicitly demonstrate how the Purcell factor is enhanced at the FabryPérot resonances of the wire metamaterial block in microwave frequency range. The experimental results are in a good agreement with theoretical and numerical estimations.

(2014) Physical review letters. 112, 10, 107403. Abstract
We present a theory of topological edge states in onedimensional resonant photonic crystals with a compound unit cell. Contrary to the conventional electronic topological states, the modes under consideration are radiative; i.e., they decay in time due to the light escape through the structure boundaries. We demonstrate that the edge states survive despite their radiative decay and can be detected both in time and frequencydependent light reflection.

(2014) Physical Review B  Condensed Matter and Materials Physics. 89, 12, 125409. Abstract
We present a theory of electronphonon interaction and phonon decay in Si nanocrystals based on sp3d5s* empirical tightbinding model and anharmonic Keating model. We demonstrate that the time of optical phonon emission by hot carriers in Si nanocrystal lies in the subpicosecond time range. However, due to the fast phonon recycling, the energy relaxation rate is determined not by the phonon emission but by the phonon decay rate. The decay rate of the optical phonon into two phonons of smaller energy is found to be in the 110 ps range. It is this anharmonic phonon decay process that may control the energy relaxation rate of excited carriers in Si nanocrystals.

(2014) Physical Review A  Atomic, Molecular, and Optical Physics. 89, 3, 032508. Abstract
An electric dipole placed in an anisotropic medium experiences a torque due to the induced polarization of the medium. The torque tends to align the dipole in the appropriate direction determined by the medium properties. Here we present simple quantitative theory of this effect and predict splitting of the emission spectrum lines of the elementary quantum emitter in an anisotropic environment due to the selfinduced torque.

(2014) Journal of Experimental and Theoretical Physics. 118, 2, p. 205216 Abstract
The time dependence of correlations between the photons emitted from a microcavity with an embedded quantum dot under incoherent pumping is studied theoretically. Analytic expressions for the secondorder correlation function g ^{(2)}(t) are presented in strong and weak coupling regimes. The qualitative difference between the incoherent and coherent pumping schemes in the strong coupling case is revealed: under incoherent pumping, the correlation function demonstrates pronounced Rabi oscillations, but in the resonant pumping case, these oscillations are suppressed. At high incoherent pumping, the correlations decay monoexponentially. The decay time nonmonotonically depends on the pumping value and has a maximum corresponding to the selfquenching transition.

(2014) ACS Photonics. 1, 2, p. 101105 Abstract
We propose a simple realization of topological edge states in zigzag chains of plasmonic nanoparticles, mimicking the Kitaev model of Majorana fermions. We demonstrate the onetoone correspondence between the coupled dipole equations in the zigzag plasmonic chain and the BogoliubovdeGennes equations for the quantum wire on top of superconductor and support the analytical theory by the fullwave electromagnetic simulations. We reveal that localized plasmons can be excited selectively at both edges of the zigzag chain of plasmonic nanoparticles depending on the incident plane wave polarization. (Chemical Presented).

(2014) Nature Communications. 5, 3226. Abstract
The routing of light in a deep subwavelength regime enables a variety of important applications in photonics, quantum information technologies, imaging and biosensing. Here we describe and experimentally demonstrate the selective excitation of spatially confined, subwavelength electromagnetic modes in anisotropic metamaterials with hyperbolic dispersion. A localized, circularly polarized emitter placed at the boundary of a hyperbolic metamaterial is shown to excite extraordinary waves propagating in a prescribed direction controlled by the polarization handedness. Thus, a metamaterial slab acts as an extremely broadband, nearly ideal polarization beam splitter for circularly polarized light. We perform a proof of concept experiment with a uniaxial hyperbolic metamaterial at radiofrequencies revealing the directional routing effect and strong subwavelength λ/300 confinement. The proposed concept of metamaterialbased subwavelength interconnection and polarizationcontrolled signal routing is based on the photonic spin Hall effect and may serve as an ultimate platform for either conventional or quantum electromagnetic signal processing.

(2014) CLEO. Abstract
Interference, one of the major physical phenomena, relies on coherent superposition of waves, undertaking different phase lag. Considering vectorial nearfields structure, the fundamental concept was reconsidered, reformulated, and demonstrated at optical and radio frequencies.
2013

(2013) Nature Photonics. 7, 12, p. 958967 Abstract
Electromagnetic metamaterials, artificial media created by subwavelength structuring, are useful for engineering electromagnetic space and controlling light propagation. Such materials exhibit many unusual properties that are rarely or never observed in nature. They can be employed to realize useful functionalities in emerging metadevices based on light. Here, we review hyperbolic metamaterialsone of the most unusual classes of electromagnetic metamaterials. They display hyperbolic (or indefinite) dispersion, which originates from one of the principal components of their electric or magnetic effective tensor having the opposite sign to the other two principal components. Such anisotropic structured materials exhibit distinctive properties, including strong enhancement of spontaneous emission, diverging density of states, negative refraction and enhanced superlensing effects.

(2013) Physical Review A  Atomic, Molecular, and Optical Physics. 88, 5, 053819. Abstract
We present a robust approach for interpreting the physics of Fano resonances in planar oligomer structures of both metallic and dielectric nanoparticles. We reveal a key mechanism for Fano resonances by demonstrating that such resonances can be generated purely from the interference of nonorthogonal collective eigenmodes, which are clearly identified based on the coupleddipole approximation. We prove analytically a general theorem to identify the number of collective eigenmodes that can be excited in ringtype nanoparticle oligomers and further demonstrate that no darkmode excitation is necessary for the existence of Fano resonances in symmetric oligomers. As a consequence, we unify the understanding of Fano resonances for both plasmonic and alldielectric oligomers.

(2013) Physical Review B  Condensed Matter and Materials Physics. 88, 15, 155304. Abstract
We report on investigations of optical carrier generation in silicon nanocrystals embedded in an SiO_{2} matrix. Carrier relaxation and recombination processes are monitored by means of timeresolved induced absorption, using a conventional femtosecond pumpprobe setup for samples containing different average sizes of nanocrystals (d_{NC} = 2.55.5 nm). The electronhole pairs generated by the pump pulse are probed by a second pulse over a broad spectral range (E_{probe} = 0.951.35 or 1.63.25 eV), by which information on excited states is obtained. Under the same excitation conditions, we observe that the induced absorption intensity in the nearinfrared range is a factor of ∼10 higher than in the visible range. To account for these observations, we model the spectral dependence of the induced absorption signal using an empirical sp3d5s^{*} tightbinding technique, by which the spectrum can be well reproduced up to a certain threshold. For probe photon energies above this threshold (dependent on nanocrystal size), the induced absorption signal is found to feature a longstanding component, whereas the induced absorption signal for probe photon energies below this value vanishes within 0.5 ns. We explain this by selftrapping of excitons on surfacerelated states.

(2013) Physical review letters. 111, 3, 036804. Abstract
Optical forces constitute a fundamental phenomenon important in various fields of science, from astronomy to biology. Generally, intense external radiation sources are required to achieve measurable effects suitable for applications. Here we demonstrate that quantum emitters placed in a homogeneous anisotropic medium induce selftorques, aligning themselves in the welldefined direction determined by an anisotropy, in order to maximize their radiation efficiency. We develop a universal quantummechanical theory of selfinduced torques acting on an emitter placed in a material environment. The theoretical framework is based on the radiation reaction approach utilizing the rigorous Langevin local quantization of electromagnetic excitations. We show more than 2 orders of magnitude enhancement of the selftorque by an anisotropic metamaterial with hyperbolic dispersion, having negative ratio of permittivity tensor components, in comparison with conventional anisotropic crystals with the highest naturally available anisotropy.

(2013) 2012 7th European Microwave Integrated Circuit Conference (EuMIC 2012). p. 838840 Abstract
We demonstrate how the medium with the hyperbolic isofrequency surfaces in the wavevector space can be realized by twodimensional artificial transmission lines. The peculiar character of wave propagation in such a hyperbolic medium is visualized by the study of the crosslike emission pattern of a current source. Our results are supported by the direct solution of the Kirchhoff equations and an analytical theory.

(2013) Physics of the Solid State. 55, 5, p. 905923 Abstract
The subject of the review is the diffraction of an electromagnetic wave on a periodic condensed matter where the Bragg condition is satisfied at the frequency of resonance excited in this medium. The Bragg systems known as resonant photonic crystals in general have been considered, and the propagation, reflection, transmission, and diffraction of electromagnetic radiation in different objects(I) periodic quantumwell structures near the exciton resonance, (II) optical lattices of atoms cooled in a laser field, and (III) bulk crystals and multilayers with gammaray resonance intranuclear transitionshave been described in a unified context. The main attention has been paid to the steadystate linear diffraction, including resonant reflection and transmission, which is the best studied and allows a comparison of the three aforementioned systems with the aim of revealing specific characteristics and common features. A characteristic common property of the considered systems is the suppression of nonradiative channels and an inhomogeneous broadening of the resonance frequency. The second fundamental property of resonant photonic crystals is that the interaction of light with resonant excitation can occur in two regimes depending on the thickness of the sample. In the superradiant regime realized for a small number of resonant layers N (fine structures), the height of the peak and halfwidth of the reflection spectrum monotonically increase with increasing value of N. With a further increase in N, there occurs a transition to a photoniccrystal regime where the halfwidth of the reflection spectrum is saturated, which manifests itself in the form of an optical stop band. The theoretical description is illustrated by experimental spectra measured for all three resonant Bragg systems.

(2013) Journal of Applied Physics. 113, 14, 144311. Abstract
We present experimental and theoretical study of light reflection spectra from hybrid structures formed by Ge_{2}Sb_{2}Te_{5} chalcogenide film on top of 3D opaline photonic crystal. We demonstrate the presence of diffraction anomalies (Wood anomalies) in the spectra. These anomalies are caused by the light scattering on the hybrid structure surface of hexagonal symmetry. To interpret the experimental results, we develop a qualitative theoretical model, taking into account the dispersion of quasiwaveguide modes supported by the surface layer of the hybrid structure. We consider the conditions for the coupling between the Bragg resonances associated with the diffraction of light on the 3D opal lattice and the resonances due to Wood anomalies.


(2013) New Journal of Physics. 15, 025016. Abstract
A theory of nonlinear emission of localized excitons coupled to the optical mode of the microcavity is presented. Numerical results are compared with analytical ones. The effects of excitonexciton interaction within the quantum dots and with the reservoir formed by nonresonant pumping are considered. It is demonstrated that the nonlinearity due to the interaction strongly affects the shape of the emission spectra. The collective superradiant mode of the excitons is shown to be stable against the nonlinear effects.

(2013) 2012 42nd European Microwave Conference (EuMC 2012). p. 12181220 Abstract
We demonstrate how the medium with the hyperbolic isofrequency surfaces in the wavevector space can be realized by twodimensional artificial transmission lines. The peculiar character of wave propagation in such a hyperbolic medium is visualized by the study of the crosslike emission pattern of a current source. Our results are supported by the direct solution of the Kirchhoff equations and an analytical theory.

(2013) ECS Journal of Solid State Science and Technology. 2, 6, p. R97R99 Abstract
Due to the covalent character of siliconcarbon (SiC) bond, Clinked molecules on the silicon quantum dot (SiQD) surface lead to dramatic changes in wavefunctions of the excited electronhole pairs. Some of the optical transitions are strongly modified and attain direct bandgaplike character, giving rise to bright phononless fast decaying emission, while many other transitions keep their typical indirect bandgap character. It appears that in Cterminated SiQDs, with diameter larger than ∼2 nm, the most efficient recombination occurs from states slightly above the ground state. This leads to thermal activation of the fast emission, dominating the photoluminescence from these SiQDs. On the other hand, in the smallest SiQDs of less than 2 nm, the lowest excited states have the direct bandgaplike character and therefore their emission becomes gradually dominant at lower temperatures, as indeed supported by our experimental observations.

(2013) Semiconductors. 47, 2, p. 183202 Abstract
The main experimental results of studies of the photoluminescence of silicon nanocrystals and theoretical methods developed for the description of optical processes occurring in them are reviewed. Special attention is focused on silicon nanocrystals in the SiO_{2} matrix that were the object of most of the studies. Two fundamental theoretical methods described in detail are the multiband effectivemass method and the tightbinding method which have found wide application in simulating various processes occurring in nanostructures. A phenomenological model for excitons selftrapped on the surface of oxidized silicon nanocrystals, which has been recently developed on the basis of experimental results obtained by femtosecond spectroscopy, is reported.

(2013) Physical Review B  Condensed Matter and Materials Physics. 87, 3, 035136. Abstract
We study theoretically the enhancement of spontaneous emission in wire metamaterials. We analyze the dependence of the Purcell factor on the wire dielectric constant for both electric and magnetic dipole sources and find an optimal value of the dielectric constant for maximizing the Purcell factor for the electric dipole. We obtain analytical expressions for the Purcell factor and also provide estimates for the Purcell factor in realistic structures operating in both microwave and optical spectral ranges.

(2013) Light: Science and Applications. 2, JANUARY, e47. Abstract
Colloidal semiconductor quantum dots (QDs) constitute a perfect material for inkjet printable large area displays, photovoltaics, lightemitting diode, bioimaging luminescent markers and many other applications. For this purpose, efficient light emission/ absorption and spectral tunability are necessary conditions. These are currently fulfilled by the direct bandgap materials. SiQDs could offer the solution to major hurdles posed by these materials, namely, toxicity (e.g., Cd, Pb or Asbased QDs), scarcity (e.g., QD with In, Se, Te) and/or instability. Here we show that by combining quantum confinement with dedicated surface engineering, the biggest drawback of Sithe indirect bandgap naturecan be overcome, and a 'direct bandgap' variety of SiQDs is created. We demonstrate this transformation on chemically synthesized SiQDs using stateoftheart optical spectroscopy and theoretical modelling. The carbon surface termination gives rise to drastic modification in electron and hole wavefunctions and radiative transitions between the lowest excited states of electron and hole attain 'direct bandgaplike' (phononless) character. This results in efficient fast emission, tunable within the visible spectral range by QD size. These findings are fully justified within a tightbinding theoretical model. When the C surface termination is replaced by oxygen, the emission is converted into the wellknown red luminescence, with microsecond decay and limited spectral tunability. In that way, the 'direct bandgap' SiQDs convert into the 'traditional' indirect bandgap form, thoroughly investigated in the past.
2012

(2012) Physical Review B  Condensed Matter and Materials Physics. 86, 20, 205304. Abstract
We study the reflection of polarized optical pulses from resonant photonic structures formed by periodic, Fibonacci, and gradient sequences of quantum wells. The form and polarization of the reflected pulse are shown to be determined by the structure design and optical length. In structures with periodic quantum well arrangement, the response to ultrashort pulse is an optical signal with a sharp rise followed by an exponential decay or Bessel beats depending on the structure length. The duration of reflected pulses nonmonotonically depends on the number of quantum wells reaching the minimum for a certain structure length which corresponds to the transition from superradiant to photoniccrystalline regime. We also study the conversion of pulse polarization in the longitudinal external magnetic field which splits the exciton resonance. Comparing periodic, Fibonacci, and gradient structures we show that the latter are more efficient for the conversion from linear to circular polarization.

(2012) Journal of Applied Physics. 112, 7, 073116. Abstract
We demonstrate how to realize an indefinite media with hyperbolic isofrequency surfaces in wavevector space by employing twodimensional metamaterial transmission lines. We classify different types of such media, and visualize the peculiar character of wave propagation by study of the crosslike emission pattern of a current source placed in the lattice center. Our results are supported by a solution of the Kirchhoff equations, an analytical theory, and experimental data.

(2012) Physical Review A  Atomic, Molecular, and Optical Physics. 86, 3, 033826. Abstract
The rate of spontaneous emission is known to depend on the environment of a emitter, and the enhancement of onephoton emission in a resonant cavity is known as the Purcell effect. Here we develop a theory of spontaneous twophoton emission for a general electromagnetic environment including inhomogeneous dispersive and absorptive media. This theory is used to evaluate the twophoton Purcell enhancement in the vicinity of metallic nanoparticles and demonstrates that the surfaceplasmon resonances supported by these particles can increase the emission rate by more than two orders of magnitude. The control over twophoton Purcell enhancement given by tailored nanostructured environments could provide an emitter with any desired spectral response and may serve as an ultimate route for designing light sources with novel properties.

(2012) Physical Review A  Atomic, Molecular, and Optical Physics. 86, 2, 023848. Abstract
We revisit the problem of the electromagnetic Green function for homogeneous hyperbolic media, where longitudinal and transverse components of the dielectric permittivity tensor have different signs. We analyze the dipole emission patterns for both dipole orientations with respect to the symmetry axis and for different signs of dielectric constants, and show that the emission pattern is highly anisotropic and has a characteristic crosslike shape: the waves are propagating within a certain cone and are evanescent outside this cone. We demonstrate the coexistence of the conelike pattern due to emission of the extraordinary TMpolarized waves and elliptical pattern due to emission of ordinary TEpolarized waves. We find a singular complex term in the Green function, proportional to the δ function and governing the photonic density of states and Purcell effect in hyperbolic media.

(2012) Physica Status Solidi (C) Current Topics in Solid State Physics. 9, 7, p. 15571559 Abstract
A periodic multiple quantum well GaAs/AlGaAs structure was designed, grown and characterized in order to reveal resonant features in optical spectra when the Bragg resonance was tuned to the first or second quantum state of the heavyhole excitonpolaritons in the quantum wells. We observed a superradiant optical mode formed by the quantum well excitons under double resonance condition, i.e. when the excitonpolariton and Bragg resonances are met at the same frequency. It is manifested in a strong and wide reflection and electroreflection band.

(2012) Physical Review B  Condensed Matter and Materials Physics. 86, 3, 035148. Abstract
We study theoretically the dramatic enhancement of spontaneous emission in metamaterials with the hyperbolic dispersion modeled as a cubic lattice of anisotropic resonant dipoles. We analyze the dependence of the Purcell factor on the source position in the lattice unit cell and demonstrate that the optimal emitter positions needed to achieve large Purcell factors and Lamb shifts are in the local field maxima. We show that the calculated Green function has a characteristic crosslike shape, spatially modulated due to the structural discreteness. Our basic microscopic theory provides fundamental insights into the rapidly developing field of hyperbolic metamaterials.

(2012) Physical Review B  Condensed Matter and Materials Physics. 86, 3, 035324. Abstract
We demonstrate that confinementinduced intervalley splittings of electron energy levels in PbSe and PbS nanocrystals are sensitive to the arrangement of atoms within a nanocrystal. The splittings are strongly suppressed for stoichiometric nanocrystals of T _{d} point symmetry lacking a center of inversion as opposed to nonstoichiometric nanocrystals of O _{h} point symmetry having an inversion center. Our findings are supported by both atomistic sp3d5s ^{*} tightbinding calculations and a symmetry analysis.

(2012) Physical Review B  Condensed Matter and Materials Physics. 85, 16, 161409. Abstract
We report results of timeresolved induced absorption (IA) spectroscopy on Si nanocrystals (Si NCs) embedded in a SiO _{2} matrix. In line with theoretical modeling, the IA amplitude decreases with probing photon energy, however only until a certain threshold value. For larger photon energies, an increase of IA is observed. This unexpected behavior is interpreted in terms of the selftrapped exciton state whose formation in Si NCs was put forward some time ago based on theoretical considerations. Here, we present a direct experimental confirmation of this supposition.

(2012) Physical Review B  Condensed Matter and Materials Physics. 85, 8, 085432. Abstract
We study the phononassisted intraband relaxation of electrons and holes confined in Si nanocrystals. The rates of relaxation processes are calculated as functions of the nanocrystal size and of the temperature. It occurs that the main contribution to the relaxation is provided by the mechanism where a single acoustic and a number of optical phonons, which are necessary to compensate the energy difference between the quantized charge carrier levels, are involved. We show that the phononassisted transitions between neighboring, sizequantized levels occur typically on a picosecond time scale, but vary over several orders of magnitude with the nanocrystal size. This results in a multiexponential decay of the carrier populations averaged over an ensemble of the nanocrystals with a given size distribution. When the nanocrystal size is reduced and more than two phonons are required for the transition, there is a qualitative difference in the behavior of the transition probabilities between the electrons and the holes. Whereas the electron transition times strongly oscillate around approximately the same mean values in the picosecond range with some drops toward nanoseconds, there is a clearly pronounced tendency of the relaxation time increase into the nanosecond time range for the hole transitions when the nanocrystal size is decreased. The increase of the temperature leads to a moderate decrease of the relaxation times but does not change the picture qualitatively.

(2012) Physical Review B  Condensed Matter and Materials Physics. 85, 7, 075311. Abstract
A theory of entangled photon emission from quantum dot in microcavity under continuous and pulsed incoherent pumping is presented. It is shown that the timeresolved twophoton correlations drastically depend on the pumping mechanism: The continuous pumping quenches the polarization entanglement and strongly suppresses photon correlation times. Analytical theory of the effect is presented.

(2012) Physics Letters, Section A: General, Atomic and Solid State Physics. 376, 3, p. 185187 Abstract
We study the spontaneous emission of a dipole emitter imbedded into a layered metaldielectric metamaterial. We demonstrate ultrahigh values of the Purcell factor in such structures due to a high density of states with hyperbolic isofrequency surfaces. We reveal that the traditional effectivemedium approach greatly underestimates the value of the Purcell factor due to the presence of an effective nonlocality, and we present an analytical model which agrees well with numerical calculations.

(2012) Quantum Electronics and Laser Science Conference, QELS 2012. Abstract
We have performed rigorous dispersion analysis and showed clearly impact of nonlocality on properties of multilayered metaldielectric metamaterial. The main discovered effect is an appearance of additional extraordinary waves in the metamaterial which leads to the splitting of the TMpolarized beam at the airmetamaterial interface. Also, we have studied surface modes and Purcell effect in these metamaterials.

(2012) Nature Communications. 3, 914. Abstract
Light localization in disordered systems and Bragg scattering in regular periodic structures are considered traditionally as two entirely opposite phenomena: disorder leads to degradation of coherent Bragg scattering whereas Anderson localization is suppressed by periodicity. Here we reveal a nontrivial link between these two phenomena, through the Fano interference between Bragg scattering and disorderinduced scattering, that triggers both localization and delocalization in random systems. We find unexpected transmission enhancement and spectrum inversion when the Bragg stopbands are transformed into the Bragg passbands solely owing to disorder. Fano resonances are always associated with coherent scattering in regular systems, but our discovery of disorderinduced Fano resonances may provide novel insights into many features of the transport phenomena of photons, phonons, and electrons. Owning to ergodicity, the Fano resonance is a fingerprint feature for any realization of the structure with a certain degree of disorder.
2011

(2011) Physics of the Solid State. 53, 9, p. 17531760 Abstract
We have studied theoretically the Purcell factor which characterizes a change in the emission rate of an electric or magnetic dipole embedded in the center of a spherical cavity. The main attention is paid to the analysis of cavities with radii small compared to the wavelength. It is shown that the Purcell factor in small metallic cavities varies in a wide range depending on the ratio of the cavity size to the skin depth.

(2011) Physical Review A  Atomic, Molecular, and Optical Physics. 84, 2, 023807. Abstract
We study the radiative decay and Purcell effect for a finitesize dipole emitter placed in a homogeneous uniaxial medium. We demonstrate that the radiative rate is strongly enhanced when the signs of the medium longitudinal and transverse dielectric constants are opposite, and that the isofrequency contour corresponds to a hyperbolic medium. We reveal that the Purcell enhancement factor remains finite even in the absence of losses and that it depends on the emitter size.

(2011) Physica Status Solidi (C) Current Topics in Solid State Physics. 8, 3, p. 985990 Abstract
Energy relaxation of hot electrons and holes confined in silicon nanocrystals embedded in SiO_{2} matrix is studied theoretically. Phononassisted transitions rates strongly depend on nanocrystal diameter ranging from 10^{8} s^{1} to 10^{12} s^{1}. The Augerlike transitions are found to be considerably faster and lead to rapid energy exchange within electronhole pair.

(2011) Physica Status Solidi (C) Current Topics in Solid State Physics. 8, 3, p. 10331037 Abstract
Here we propose a possible mechanism of fast Er^{3+} ions excitation in SiO_{2} matrix with Si nanocrystals. We show that the presence of Si nanocrystals allows for nonresonant optical pumping of erbium ions by virtual Auger transition, which is the second order process via an intermediate virtual state: the first step is the optical transition inside the Si NC, and the second one is Auger excitation of Er^{3+} ion accompanied by intraband transition of the confined carrier. This mechanism of excitation can take place when the energy of photon absorbed is larger than the sum of the confined electronhole ground state energy and the excitation energy of Er^{3+} ion. We have calculated the excitation crosssection as a function of the excitation energy for erbium ions situated both inside and outside the NC. We show that virtually all Er^{3+} ions inside NCs can be excited directly into the first excited state ^{4}I_{13/2} (responsible for the 1.5 μm emission) by the laser pulse of duration 510 ns. The results obtained for ions located outside NCs demonstrate the efficiency of the virtual excitation Auger process for transition of erbium ions into the higher excited states. 1.5 μm PL appears in this case as a result of nonradiative relaxation of excited ions down to the ^{4}I_{13/2} state. Correspondingly, the rise time of the 1.5 μm PL should be about several microseconds. The crosssections calculated demonstrate the efficiency of such Auger process.

(2011) Applied Physics Letters. 98, 7, 073112. Abstract
A periodic multiple quantum well GaAs/AlGaAs structure was designed, grown, and characterized in order to reveal resonant features in optical spectra when the Bragg resonance was tuned to the second quantum state x(e2hh2) of the heavyhole excitonpolaritons in the multiple quantum wells. This double resonance was demonstrated by tuning the incident angle of the light as well as by comparison with a single quantum well structure. A significant enhancement of the lightmatter interaction was observed, which manifests itself by strong resonant optical reflection and electroreflection.

(2011) Physical Review B  Condensed Matter and Materials Physics. 83, 7, 075106. Abstract
A theory of light diffraction from a planar quasicrystalline lattice with resonant scatterers is presented. Rich structure, absent in the periodic case, is found in specular reflection spectra, and interpreted as a specific kind of Wood anomaly, characteristic of quasicrystals. The theory is applied to semiconductor quantum dots arranged in Penrose tiling.
2010

(2010) Applied Physics Letters. 97, 23, 231116. Abstract
Dynamics of hot carriers confined in Si nanocrystals is studied theoretically using atomistic tight binding approach. Radiative, Augerlike, and phononassisted processes are considered. The Augerlike energy exchange between electrons and holes is found to be the fastest process in the system. However, the energy relaxation of hot electronhole pair is governed by the single optical phonon emission. For a considerable number of states in small nanocrystals, singlephonon processes are ruled out by energy conservation law.

(2010) Physical Review B  Condensed Matter and Materials Physics. 82, 20, 205330. Abstract
A theory of optical emission of quantum dot arrays in quantum microcavities is developed. The regime of the strong coupling between the quantum dots and photonic mode of the cavity is considered. The quantum dots are modeled as twolevel systems. In the low pumping (linear) regime the emission spectra are mainly determined by the superradiant mode where the effective dipoles of the dots oscillate in phase. In the nonlinear regime the superradiant mode is destroyed and the emission spectra are sensitive to the parity of quantum dot number. Further increase in the pumping results in the emission line narrowing being an evidence of the lasing regime.

(2010) Physica E: LowDimensional Systems and Nanostructures. 42, 7, p. 18711895 Abstract
Discovery of quasicrystals and other deterministic aperiodic structures initiated new fields of research in solidstate photonics. In this review, we first make an overview of recently fabricated aperiodic systems, one, two and threedimensional. Then we briefly discuss clarifying and supplementing definitions of binary chains, irrational cuts through higherdimensional lattices and tiling with regular polygons or polyhedrons. A particular attention is paid to theoretical aspects of light propagation in aperiodic photonic structures, including analysis of the geometric structure factor for different systems and application of the twowave approximation. In the main part of the article we review different aspects of the optical spectroscopy of longrangeordered aperiodic systems, both nonresonant and resonant, and show its state of the art in reflection, transmission, absorption, photoluminescence and nonlinear optics. Emphasis is placed on resemblance and distinction between the third form of solid matter, aperiodic longrange ordered photonic structures, and conventional crystals or disordered materials.

(2010) JETP Letters. 90, 10, p. 683687 Abstract
We propose a Fröhlichtype electronphonon interaction mechanism for carriers confined in a nonpolar quantum dot surrounded by an amorphous polar environment. Carrier transitions under this mechanism are due to their interaction with the oscillating electric field induced by the local vibrations in the surrounding amorphous medium. We estimate the corresponding energy relaxation rate for electrons in Si nanocrystals embedded in a SiO_{2} matrix as an example. When the nanocrystal diameter is larger than 4 nm then the gaps between the electron energy levels of size quantization are narrow enough to allow for transitions accompanied by emission of a single local phonon having the energy about 140 meV. In such Si/SiO_{2} nanocrystals the relaxation time is in nanosecond range.

(2010) Semiconductors. 44, 12, p. 15371542 Abstract
The parameters of threedimensional photonic crystals based on opalVO_{2} composite films in the 1.31.6 μm spectral range important for practical applications (Telecom standard) are numerically calculated. For opal pores, the range of filling factors is established (0.250.6) wherein the composite exhibits the properties of a threedimensional insulator photonic crystal. On the basis of the opalVO_{2} composites, threedimensional photonic film crystals are synthesized with specified parameters that provide a maximum shift of the photonic band gap in the vicinity of the wavelength ~1.5 μm (~170 meV) at the semiconductormetal transition in VO_{2}.
2009

(2009) Physical Review B  Condensed Matter and Materials Physics. 80, 11, 115314. Abstract
We have theoretically studied propagation of excitonpolaritons in deterministic aperiodic multiplequantumwell structures, particularly, in the Fibonacci and ThueMorse chains. The attention is concentrated on the structures tuned to the resonant Bragg condition with twodimensional quantumwell exciton. Depending on the number of wells, the superradiant either photonicquasicrystal regimes are realized in these aperiodic structures. For moderate values of the exciton nonradiative damping rate Γ, the developed theory based on the twowave approximation allows one to perceive and describe analytically the exact transfermatrix computations for transmittance and reflectance spectra in the whole frequency range except for a narrow region near the exciton resonance ω0. In this region the optical spectra and the excitonpolariton dispersion demonstrate scaling invariance and selfsimilarity which can be interpreted in terms of the "bandedge" cycle of the trace map, in the case of Fibonacci structures, and in terms of zero reflection frequencies, in the case of ThueMorse structures. With decreasing Γ, in the whole allowed polariton band the twowave approximation stops to be valid, and a transition occurs from Blochlike to localized states, with modes closer to ω0 becoming localized first.

(2009) Journal of Experimental and Theoretical Physics. 108, 5, p. 836844 Abstract
Emission spectra of quantum dot arrays in zerodimensional microcavities are studied theoretically. It is shown that their form is determined by the competition between collective superradiant mode formation and inhomogeneous broadening. A random sources method is used to calculate the photoluminescence spectra from an nonresonant pumped microcavity, and a standard diagram technique is used to provide a microscopic justification for the random sources method. The emission spectra of a microcavity are analyzed taking into account the spread of exciton energy due to inhomogeneous distribution of quantum dots and tunneling between them. It is demonstrated that the luminescence spectra of strongly tunnelcoupled quantum dots are sensitive to the dot positions, and the collective mode can (under certain conditions) be stabilized by random tunneling links.

(2009) Physica E: LowDimensional Systems and Nanostructures. 41, 6, p. 969971 Abstract
Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots (QDs) in SiO_{2} matrix is considered. Interaction of confined holes with optical phonons is studied. The HuangRhys factor governing intraband transitions induced by this interaction is calculated. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.

(2009) Optics Express. 17, 8, p. 68136828 Abstract
A detailed experimental and theoretical study of the linear and nonlinear optical properties of different Fibonaccispaced multiplequantum well structures is presented. Systematic numerical studies are performed for different average spacing and geometrical arrangement of the quantum wells. Measurements of the linear and nonlinear (carrier density dependent) reflectivity are shown to be in good agreement with the computational results. As the pump pulse energy increases, the excitationinduced dephasing broadens the exciton resonances resulting in a disappearance of sharp features and reduction in peak reflectivity.

(2009) 2009 Conference on Lasers and ElectroOptics & Quantum Electronics and Laser Science Conference (CLEO/QELS 2009). Abstract
Quasicrystals based on the excitonic resonances of GaAs/AlGaAs quantum wells were grown with spacings that satisfy a Fibonacci sequence. Linear and nonlinear reflectivity and photoluminescence measurements were performed, agreeing quite well with theory.
2008

(2008) Optics Express. 16, 26, p. 2151221521 Abstract
An instability in the growth of nonperiodic InGaAs/GaAs multiple quantum well samples, ordinarily of highquality when grown with equal periods of order of half the wavelength of light in the material, leads to a dramatic microscopic, selforganized surface grating. This effect was discovered while growing quantum wells with two unequal barrier lengths arranged in a Fibonacci sequence to form an optical quasicrystal. A laser beam incident normal to the surface of the sample is diffracted into a propellershaped pattern. The sample surface has a distinctly cloudy appearance when viewed along one crystal axis but is mirrorlike when the sample is rotated 90°. The instability results in a fivefold increase in the absorption linewidth of the heavyhole exciton transition. Atomic force microscopy, transmission electron microscopy, and scanning electron microscopy were used to study the samples.

(2008) Optics Express. 16, 20, p. 1538215387 Abstract
The fabrication and characterization of lightemitting onedimensional photonic quasicrystals based on excitonic resonances is reported. The structures consist of highquality GaAs/AlGaAs quantum wells grown by molecularbeam epitaxy with wavelengthscale spacings satisfying a Fibonacci sequence. The polaritonic (resonant lightmatter coupling) effects and light emission originate from the quantum well excitonic resonances. Measured reflectivity spectra as a function of detuning between emission and Bragg wavelength are in good agreement with excitonic polariton theory. Photoluminescence experiments show that active photonic quasicrystals, unlike photonic crystals, can be good light emitters: While their longrange order results in a stopband similar to that of photonic crystals, the lack of periodicity results in strong emission.

(2008) Solid State Communications. 146, 34, p. 143147 Abstract
Transmission, reflection and absorption of electromagnetic radiation and photon dispersion law for 2D photonic crystals with superconducting elements are studied. The calculation of the optical properties of photonic crystals is performed by layerbylayer KorringaKohnRostoker techniques. The results of numerical calculations carried out for an array of superconducting cylinders have been understood in terms of a simple analytical model. The controlling of the optical properties of superconducting photonic crystal by temperature and magnetic fields is discussed. The variation of superconducting component density with temperature leads, particularly, to significant reduction of the transmission peaks and even to a nonmonotonic behavior of some absorbance peaks.

(2008) Physical Review B  Condensed Matter and Materials Physics. 77, 11, 113306. Abstract
We propose a resonant onedimensional quasicrystal, namely, a multiple quantum well (MQW) structure satisfying the Fibonaccichain rule with the golden ratio between the long and short interwell distances. The resonant Bragg condition is generalized from the periodic to Fibonacci MQWs. A dispersion equation for exciton polaritons is derived in the twowave approximation; the effective allowed and forbidden bands are found. The reflection spectra from the proposed structures are calculated as a function of the well number and detuning from the Bragg condition.

(2008) Physical Review B  Condensed Matter and Materials Physics. 77, 7, 075315. Abstract
A defectassisted mechanism of multiphonon intraband carrier relaxation in semiconductor quantum dots, where the carrier is found in a coherent superposition of the initial, final, and defect states, is proposed. It is shown that this mechanism is capable of explaining the observed trends in temperature dependences of the intraband relaxation rates for PbSe and CdSe colloidal nanocrystal quantum dots.
2007

(2007) Physics of the Solid State. 49, 10, p. 19771987 Abstract
The excitonpolariton transfer and absorption in regular and disordered structures with a finite number of quantum wells are studied theoretically. The transfer matrix method is invoked in the exciton resonance region to calculate the reflectivity, transmissivity, and absorptivity spectra, as well as the integrated absorptivity as a function of the γ/Γ _{0} ratio of the parameters of nonradiative and radiative damping of quasitwodimensional excitons. It is shown that the integrated absorptivity as a function of γ (temperature) follows a universal pattern, more specifically, it increases monotonically from zero at γ = 0 to saturate at γ/Γ _{0} 1. Because the excitonpolariton absorption being single mode, the integrated absorptivity in Bragg quantumwell structures is substantially lower than that in shortperiod structures, in which absorption involves the whole spectral multitude of modes. The intrawell disorder associated with fluctuations in the frequencies of exciton excitation in quantum wells enhances the integrated absorptivity to the level typical of light absorption with no resonance among excitons of different quantum wells. The interwell disorder originating from fluctuations in quantumwell separation likewise leads to an increase in the integrated absorptivity.

(2007) Physics of the Solid State. 49, 9, p. 17921802 Abstract
The optical spectra of resonant Bragg and quasiBragg quantumwell structures are studied theoretically. The existence of special frequencies in the reflectance and absorbance spectra at which the reflectance or absorbance does not depend on the number of quantum wells in a structure is explained analytically. It is shown that the reflectance and absorbance spectra of structures in which the quantumwell width substantially exceeds the exciton Bohr radius also contain special frequencies and that the smooth spectral component is determined primarily by the interaction of the light wave with the quantumwell groundstate exciton.

(2007) Physics of the Solid State. 49, 2, p. 360365 Abstract
The spectra of specular reflection and diffraction of light for a resonant twodimensional photonic crystal consisting of semiconductor cylinders embedded in a dielectric matrix, as well as the exciton–polariton band structure of this crystal, are studied theoretically. It is shown that specular reflection of light from a photonic crystal can be considerably enhanced by diffraction in the photonic crystal and reflection from its inner boundary with vacuum.
2006

(2006) Physics of the Solid State. 48, 9, p. 18141819 Abstract
The optical reflectance spectra of resonant Bragg quantumwell structures are studied theoretically. The existence of two special frequencies in the spectra at which the reflectance depends only weakly on the number of quantum wells in the structure is explained analytically. The effect of nonradiative exciton damping on the reflectance spectra in the vicinity of the special frequencies is analyzed. It is shown that the inclusion of the dielectric contrast leads to the appearance of a third special frequency, at which the contributions to the reflectance due to the dielectric contrast and exciton resonance completely cancel each other.

(2006) Physics of the Solid State. 48, 3, p. 581588 Abstract
The theory of the excitonpolariton band structure of a resonant threedimensional photonic crystal is developed for an arbitrary dielectric contrast and an arbitrary effective mass of an exciton excited in a composite material. The calculation is performed for a periodic array of semiconductor balls embedded in a dielectric matrix. The position of the lower polariton dispersion branches is shown to depend monotonically on the exciton effective mass and to be governed by the interaction of light with the first several states of a mechanical exciton quantumconfined within each ball. The effect of excitonic states on the band gap of a photonic crystal in the [001] direction is considered analytically in terms of a twowave approximation.