arXiv subjects

Yu. S. Kivshar

Publications and source records attributed to Yu. S. Kivshar.

17 recordsLinked to original sources

arXiv2018

Bound states in the continuum and Fano resonances in the strong mode coupling regime

The study of resonant dielectric nanostructures with high refractive index is a new research direction in nanoscale optics and metamaterial-inspired nanophotonics. Because of the unique optically-induced electric and magnetic Mie resonances, high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications. Here we study strong coupling between modes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances when resonator's aspect ratio varies. We demonstrate that strong mode coupling results in resonances with high quality factors, which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich-Wintgen scenario of destructive interference. We explain the physics of these states in terms of multipole decomposition and show that their appearance is accompanied by drastic change of the far-field radiation pattern. We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra. Our theoretical findings are confirmed by microwave experiments for the scattering of a high-index cylindrical resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high quality factor helps to extend substantially functionalities of all-dielectric nanophotonics that opens new horizons for active and passive nanoscale metadevices.

physics.optics↗

arXiv2018

Observation and control of nonlinear electromagnetic topological edge states

Topological photonics has recently emerged as a route to realize robust optical circuitry, and nonlinear effects are expected to enable tunability of topological states with the light intensity. Here we realize experimentally nonlinear self-induced spectral tuning of the electromagnetic topological edge states in an array of coupled nonlinear resonators in a pump-probe experiment. In a weakly nonlinear regime, we observe that resonators frequencies exhibit spectral shifts, that are concentrated mainly at the edge mode 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 to unstable regimes.

physics.optics↗

arXiv2016

Enhanced photonic spin Hall effect with subwavelength topological edge states

Photonic structures offer unique opportunities for controlling light-matter interaction, including the photonic spin Hall effect associated with the transverse spin-dependent displacement of light that propagates in specially designed optical media. However, due to small spin-orbit 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 near-field 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 a topology-enhanced spin Hall effect, and also analyse the robustness of the photonic edge states against the long-ranged coupling.

cond-mat.mes-hall↗

arXiv2015

Enhancement of magnetic resonance imaging with metasurfaces

Magnetic resonance imaging (MRI) is the cornerstone technique for diagnostic medicine, biology, and neuroscience. This imaging method is highly innovative, noninvasive and its impact continues to grow. It can be used for measuring changes in the brain after enhanced neural activity, detecting early cancerous cells in tissue, as well as for imaging nanoscale biological structures, and controlling fluid dynamics, and it can be beneficial for cardiovascular imaging. The MRI performance is characterized by a signal-to-noise ratio, however the spatial resolution and image contrast depend strongly on the scanner design. Here, we reveal how to exploit effectively the unique properties of metasurfaces for the substantial improvement of MRI efficiency. We employ a metasurface created by an array of wires placed inside the MRI scanner under an object, and demonstrate a giant enhancement of the magnetic field by means of subwavelength near-field manipulation with the metasurface, thus strongly increasing the scanner sensitivity, signal-to-noise ratio, and image resolution. We demonstrate experimentally this effect for a commercially available MRI scanner and a biological tissue sample. Our results are corroborated by measured and simulated characteristics of the metasurface resonator, and our approach can enhance dramatically functionalities of widely available low-field MRI devices.

physics.med-ph↗

arXiv2015

Hybrid waves localized at hyperbolic metasurfaces

We reveal the existence of a new type of surface electromagnetic waves supported by hyperbolic metasurfaces, described by a conductivity tensor with an indefinite signature. We demonstrate that the spectrum of the hyperbolic metasurface waves consists of two branches corresponding to hybrid TE-TM waves with the polarization that varies from linear to elliptic or circular depending on the wave frequency and propagation direction. We analyze the effect of losses of the surface waves and derive the corresponding analytical asymptotic expressions.

physics.optics↗

arXiv2013

Optical tweezers for vortex rings in Bose-Einstein condensates

We study formation and stabilization of vortex rings in atomic Bose-Einstein condensates. We suggest a novel approach for generating and trapping of vortex rings by 'optical tweezers'--two blue-detuned optical beams forming a toroidal void in the bulk of a magnetically or optically confined condensate cloud. We demonstrate that matter-wave vortex rings trapped within the void are energetically and dynamically stable. Our theoretical findings suggest the possibility for generation, stabilization, and nondestructive manipulation of quantized vortex rings in experimentally feasible trapping configurations.

cond-mat.quant-gas↗

arXiv2013

Self-localization of polariton condensates in periodic potentials

We predict the existence of novel spatially localized states of exciton-polariton Bose-Einstein condensates in semiconductor microcavities with fabricated periodic in-plane potentials. Our theory shows that, under the condition of continuous off-resonant pumping and losses associated with polariton decay, localization is observed for a wide range of optical pump parameters due to effective potentials self-induced by the polariton flows in the spatially periodic system. We reveal that the self-localization of exciton-polaritons in the lattice may occur both in the gaps and bands of the single-particle linear spectrum, and is dominated by the effects of gain and dissipation rather than the applied potential, in sharp contrast to the conservative condensates of ultracold alkali atoms.

cond-mat.quant-gas↗

arXiv2012

Cascaded four-wave mixing in tapered plasmonic nanoantenna

We study theoretically the cascaded four-wave mixing (FWM) in broadband tapered plasmonic nanoantennas and demonstrate a 300-fold increase in nonlinear frequency conversion detected in the main lobe of the nanoantenna far-field pattern. This is achieved by tuning the elements of the nanoantenna to resonate frequencies involved into the FWM interaction. Our findings have a potentially broad application in ultrafast nonlinear spectroscopy, sensing, on-chip optical frequency conversion, nonlinear optical metamaterials and photon sources.

physics.optics↗

arXiv2012

Nonlinear metal-dielectric nanoantennas for light switching and routing

We introduce a novel hybrid metal-dielectric nanoantenna composed of dielectric (crystalline silicon) and metal (silver) nanoparticles. A high-permittivity dielectric nanoparticle allows to achieve effective light harvesting, and nonlinearity of a metal nanoparticle controls the radiation direction. We show that the radiation pattern of such a nanoantenna can be switched between the forward and backward directions by varying only the light intensity around the level of 11 MW/cm$^2$, with the characteristic switching time of 260 fs.

physics.optics↗

arXiv2011

Multifrequency broadband tapered plasmonic nanoantennas

We suggest a novel multifrequency broadband plasmonic Yagi-Uda-type nanoantenna equipped with an array of tapered directors. Each director can be used for the excitation of the antenna by nanoemitters matched spectrally with the director resonant frequency and placed in the director near-field region. Multifrequency op- eration of nanoantennas provides tremendous opportunities for broadband emission enhancement, spectroscopy and sensing. By the principle of reciprocity, the same tapered nanoantenna architecture can be used both as a transmitter and/or as a receiver, thus being useful for creating a broadband wireless communication system.

physics.optics↗

arXiv2010

Optomechanics of liquid crystals for dynamical optical response of photonic structures

We show that the mechanical effect of light on the orientational ordering of the crystalline axis of a mesophase can be used to control the dynamics of the optical response of liquid crystal infiltrated photonic structures. The demonstration is made using a one-dimensional periodic structure whose periodicity is broken by the presence of a nematic liquid crystal defect layer. In this study we report on output light polarization and/or intensity dynamics that depends on the initial molecular ordering and incident light wavelength and intensity.

cond-mat.soft↗

arXiv2008

Spinor Bose-Einstein condensate flow past an obstacle

We study the flow of a spinor (F=1) Bose-Einstein condensate in the presence of an obstacle. We consider the cases of ferromagnetic and polar spin-dependent interactions and find that the system demonstrates two speeds of sound that are identified analytically. Numerical simulations reveal the nucleation of macroscopic nonlinear structures, such as dark solitons and vortex-antivortex pairs, as well as vortex rings in one- and higher-dimensional settings respectively, when a localized defect (e.g., a blue-detuned laser beam) is dragged through the spinor condensate at a speed larger than the second critical speed.

nlin.PS↗

arXiv2008

Nonlinear plasmonic slot waveguides

We study nonlinear modes in subwavelength slot waveguides created by a nonlinear dielectric slab sandwiched between two metals. We present the dispersion diagrams of the families of nonlinear plasmonic modes and reveal that the symmetric mode undergoes the symmetry-breaking bifurcation with the energy primarily localized near one of the interfaces. We also find that the antisymmetric mode may split into two brunches giving birth to two families of nonlinear antisymmetric modes.

physics.optics↗

arXiv2008

Macroscopic quantum self-trapping in a Bose-Josephson junction with fermions

We study the macroscopic quantum self-trapping effect in a mixture of Bose-Einstein condensate and a large number of quantum degenerate fermions, trapped in a double-well potential with a variable separation between the wells. The large number of fermions localized in each well form quasi-static impurities that affect the dynamics of the bosonic cloud. Our semi-analytical analysis based on a mean-field model shows that main features of macroscopic quantum self trapping in a pure bosonic system are radically modified by the influence of fermions, with both the onset of self-trapping and properties of the self-trapped state depending on the fermion concentration as well as on the type of inter-species interaction. Remarkably, repulsive inter-species interaction leads to population inversion of the bosonic energy levels in the trapping potential and hence to the inversion of symmetry of the macroscopic wavefunction. Realistic physical estimates are given based on experimental parameters for a $^{40}$K-$^{87}$Rb system.

cond-mat.other↗

arXiv2007

Optical Bloch oscillations in periodic structures with metamaterials

We predict that optical Bloch oscillations can be observed in layered structures with left-handed metamaterials and zero average refractive index where the layer thickness varies linearly across the structure. We demonstrate a new type of the Bloch oscillations associated with coupled surface waves excited at the interfaces between the layers with left-handed material and conventional dielectric.

physics.optics↗

arXiv2006

Zener tunneling in two-dimensional photonic lattices

We discuss the interband light tunneling in a two-dimensional periodic photonic structure, as was studied recently in experiments for optically-induced photonic lattices [H. Trompeter et al., Phys. Rev. Lett. \textbf{96}, 053903 (2006)]. We identify the Zener tunneling regime at the crossing of two Bloch bands, which occurs in a generic case of the Bragg reflection when the Bloch index crosses the edge of the irreducible Brillouin zone. Similarly, the higher-order Zener tunneling involves four Bloch bands when the Bloch index passes through a high-symmetry point on the edge of the Brillouin zone. We derive simple analytical models that describe the tunneling effect, and calculate the corresponding tunneling probabilities.

cond-mat.other↗

arXiv1995

Soliton pinning by long-range order in aperiodic systems

We investigate propagation of a kink soliton along inhomogeneous chains with two different constituents, arranged either periodically, aperiodically, or randomly. For the discrete sine-Gordon equation and the Fibonacci and Thue-Morse chains taken as examples, we have found that the phenomenology of aperiodic systems is very peculiar: On the one hand, they exhibit soliton pinning as in the random chain, although the depinning forces are clearly smaller. In addition, solitons are seen to propagate differently in the aperiodic chains than on periodic chains with large unit cells, given by approximations to the full aperiodic sequence. We show that most of these phenomena can be understood by means of simple collective coordinate arguments, with the exception of long range order effects. In the conclusion we comment on the interesting implications that our work could bring about in the field of solitons in molecular (e.g., DNA) chains.

cond-mat↗