arXiv subjects

Lev A. Smirnov

Publications and source records attributed to Lev A. Smirnov.

18 recordsLinked to original sources

arXiv2025

Momentum-space non-Hermitian skin effect in an exciton-polariton system

Localization of a macroscopic number of eigenstates on a real-space boundary, known as the non-Hermitian skin effect, is one of the striking topological features emerging from non-Hermiticity. Realizing this effect typically requires periodic (lattice) systems with asymmetry of intersite coupling, which is not readily available in many physical platforms. Instead, it is meticulously engineered, e.g., in photonics, which results in complex structures requiring precise fabrication steps. Here, we propose a simpler mechanism: introducing an asymmetric, purely imaginary potential in a topologically trivial system induces momentum-space localization akin to the skin effect. We experimentally demonstrate this localization using exciton polaritons, hybrid light-matter quasi-particles in a simple engineered `round box' trap, pumped by a laser pump offset from the trap center. The effect disappears if the pump is concentric with the trap. The localization persists and becomes stronger at higher densities of polaritons, when a non-equilibrium Bose-Einstein condensate is formed and the system becomes nonlinear. Our approach offers a new route to realizing skin effects in continuous, non-periodic systems and exploring the interplay of non-Hermiticity, topology, and nonlinearity in macroscopic quantum states.

physics.optics↗

arXiv2025

Atypical Chimera States in an Ensemble of Partially Mobile Particles

We study the influence of nonuniform motion of oscillators in a ring chain with nonlocal coupling on their collective dynamics and reveal the mechanism behind the emergence of an atypical chimera state in such systems. The mechanism relies on regular spatially inhomogeneous motion of oscillators, which breaks the symmetry of the effective interaction kernel. This symmetry breaking induces spatial phase correlations in the asynchronous part of the system, giving rise to nonuniformly twisted and previously unobserved coherent-incoherent-twisted states.

nlin.PS↗

arXiv2025

Kinetic description of one-dimensional stochastic dynamics with small inertia

We study single-variable approaches for describing stochastic dynamics with small inertia. The basic models we deal with describe passive Brownian particles and phase elements (phase oscillators, rotators, superconducting Josephson junctions) with an effective inertia in the case of a linear dissipation term and active Brownian particles in the case of a nonlinear dissipation. Elimination of a fast variable (velocity) reduces the characterization of the system state to a single variable and is formulated in four representations: moments, cumulants, the basis of Hermite functions, and the formal cumulant variant of the last. This elimination provides rigorous mathematical description for the overdamped limit in the case of linear dissipation and the overactive limit of active Brownian particles. For the former, we derive a low-dimensional equation system which generalizes the Ott-Antonsen Ansatz to systems with small effective inertia. In the latter case, we derive a Fokker-Planck-type equation with a forced drift term and an effective diffusion in one dimension, where the standard two-/three-dimensional mechanism is impossible. In the four considered representations, truncated equation chains are demonstrated to be utilitary for numerical simulation for a small finite inertia.

cond-mat.stat-mech↗

arXiv2025

Heterogeneity Induces Cyclops States in Kuramoto Networks with Higher-Mode Coupling

Disorder is often seen as detrimental to collective dynamics, yet recent work has shown that heterogeneity can enhance network synchronization. However, its constructive role in stabilizing nontrivial cooperative patterns remains largely unexplored. In this Letter, we show that frequency heterogeneity among oscillators can induce stable Cyclops and cluster states in Kuramoto networks with higher-mode coupling, even though these states are unstable in the identical oscillator case. Cyclops states, introduced in [Munyaev et al., Phys. Rev. Lett. 130, 107021 (2023)], feature two synchronized clusters and a solitary oscillator, requiring a delicate phase balance. Surprisingly, heterogeneity alone is sufficient to stabilize these patterns across a broad range of detuning values without needing to be compensated by other forms of disorder or external tuning. We introduce a mesoscopic collective coordinate approach that connects microscopic frequency structure, captured by the solitary oscillator's influence, with mean-field cluster-level stability. This constructive approach identifies favorable ranges of heterogeneity and suitable initial conditions for inducing robust multi-state dynamics, offering a foundation for their analysis in broader classes of heterogeneous biological and engineering networks.

nlin.CD↗

arXiv2024

Chimera states in a system of stationary and flying-through deterministic particles with an internal degree of freedom

We consider the effect of the emergence of chimera states in a system of coexisting stationary and flying-through in potential particles with an internal degree of freedom determined by the phase. All particles tend to an equilibrium state with a small number of potential wells, which leads to the emergence of a stationary chimera. An increase in the number of potential wells leads to the emergence of particles flying-through along the medium, the phases of which form a moving chimera. Further, these two structures coexist and interact with each other. In this case, an increase in the local synchronization degree of the chimera is observed in the areas of the synchronous cluster location.

nlin.CD↗

arXiv2024

Dynamics of large oscillator populations with random interactions

We explore large populations of phase oscillators interacting via random coupling functions. Two types of coupling terms, the Kuramoto-Daido coupling and the Winfree coupling, are considered. Under the assumption of statistical independence of the phases and the couplings, we derive reduced averaged equations with effective non-random coupling terms. As a particular example, we study interactions that have the same shape but possess random coupling strengths and random phase shifts. While randomness in coupling strengths just renormalizes the interaction, a distribution of the phase shifts in coupling reshapes the coupling function.

nlin.AO↗

arXiv2024

Synchronization by external periodic force in ensembles of globally coupled phase oscillators

We consider the effect of an external periodic force on chimera state in the phase oscillator model proposed by Abrams et al. [Phys. Rev. Lett, v. 101, 00319007 (2008)]. Using the Ott--Antonsen reduction the dynamical equations for the global order parameter characterizing the degree of synchronization are constructed. The regions of the global order parameter frequency locking by an external periodic force are constructed. The possibility of stable chimeras synchronization and unstable chimeras stabilization are established.

nlin.CD↗

arXiv2024

Breathing and switching cyclops states in Kuramoto networks with higher-mode coupling

Cyclops states are intriguing cluster patterns observed in oscillator networks, including neuronal ensembles. The concept of cyclops states formed by two distinct, coherent clusters and a solitary oscillator was introduced in [Munyayev {\it et al.}, Phys. Rev. Lett. 130, 107021 (2023)], where we explored the surprising prevalence of such states in repulsive Kuramoto networks of rotators with higher-mode harmonics in the coupling. This paper extends our analysis to understand the mechanisms responsible for destroying the cyclops' states and inducing new dynamical patterns called breathing and switching cyclops' states. We first analytically study the existence and stability of cyclops states in the Kuramoto-Sakaguchi networks of two-dimensional oscillators with inertia as a function of the second coupling harmonic. We then describe two bifurcation scenarios that give birth to breathing and switching cyclops states. We demonstrate that these states and their hybrids are prevalent across a wide coupling range and are robust against a relatively large intrinsic frequency detuning. Beyond the Kuramoto networks, breathing and switching cyclops states promise to strongly manifest in other physical and biological networks, including coupled theta-neurons.

nlin.CD↗

arXiv2023

Deterministic dynamics of overactive Brownian particle in 2D and 3D potential wells

We study deterministic dynamics of overactive Brownian particles in 2D and 3D potentials. This dynamics is Hamiltonian. Integrals of motion for continuous rotational symmetries are reported. The cases of 2D, axisymmetric and non-axisymmetric 3D potentials are characterized and compared to each other. The strong impact of the rotational symmetry integrals of motion on the chaotic and quasiperiodic orbits is revealed. The scattering cross section is reported for spherically symmetric Gaussian-shape potential wells and obstacles as a function of self-propulsion speed.

cond-mat.stat-mech↗

arXiv2023

Two-cluster regular states, chimeras and hyperchaos in a system of globally coupled phase oscillators with inertia

In this work, two-cluster modes are studied in a system of globally coupled Kuramoto-Sakaguchi phase oscillators with inertia. It is shown that these regimes can be of two types: with a constant intercluster phase difference rotating at the same frequency (according to the analysis, such regimes are always unstable) and with a periodically changing (taking into account the multiplicity of $2π$) phase mismatch. The issues of existence and stability, emergence and destruction of two-cluster modes are studied depending on the parameters: effective mass (responsible for inertial processes in the model system under consideration) and phase shift in the coupling function. The analytical results are confirmed and supplemented by numerical simulation of the rotators (second order) interacting globally through the mean field.

nlin.CD↗

arXiv2023

Dynamics of oscillator populations globally coupled with distributed phase shifts

We consider a population of globally coupled oscillators in which phase shifts in the coupling are random. We show that in the maximally disordered case, where the pairwise shifts are i.i.d. random variables, the dynamics of a large population reduces to one without randomness in the shifts but with an effective coupling function, which is a convolution of the original coupling function with the distribution of the phase shifts. This result is valid for noisy oscillators and/or in presence of a distribution of natural frequencies. We argue also, using the property of global asymptotic stability, that this reduction is valid in a partially disordered case, where random phase shifts are attributed to the forced units only. However, the reduction to an effective coupling in the partially disordered noise-free situation may fail if the coupling function is complex enough to ensure the multistability of locked states.

nlin.AO↗

arXiv2023

Identifying topology of leaky photonic lattices with machine learning

We show how machine learning techniques can be applied for the classification of topological phases in leaky photonic lattices using limited measurement data. We propose an approach based solely on bulk intensity measurements, thus exempt from the need for complicated phase retrieval procedures. In particular, we design a fully connected neural network that accurately determines topological properties from the output intensity distribution in dimerized waveguide arrays with leaky channels, after propagation of a spatially localized initial excitation at a finite distance, in a setting that closely emulates realistic experimental conditions.

physics.optics↗

arXiv2023

Self-steepening-induced stabilization of nonlinear edge waves at photonic valley-Hall interfaces

Localized nonlinear modes at valley-Hall interfaces in staggered photonic graphene can be described in the long-wavelength limit by a nonlinear Dirac-like model including spatial dispersion terms. It leads to a modified nonlinear Schrödinger equation for the wave field amplitude that remarkably incorporates a nonlinear velocity term. We show that this nonlinear velocity correction results in a counter-intuitive stabilization effect for relatively high-amplitude plane-wave-like edge states, which we confirm by calculation of complex-valued small-amplitude perturbation spectra and direct numerical simulation of propagation dynamics in staggered honeycomb waveguide lattices with on-site Kerr nonlinearity. Our findings are relevant to a variety of nonlinear photonic systems described by Dirac-like Hamiltonians.

physics.optics↗

arXiv2021

Gradient catastrophe of nonlinear photonic valley-Hall edge pulses

We derive nonlinear wave equations describing the propagation of slowly-varying wavepackets formed by topological valley-Hall edge states. We show that edge pulses break up even in the absence of spatial dispersion due to nonlinear self-steepening. Self-steepening leads to the previously-unattended effect of a gradient catastrophe, which develops in a finite time determined by the ratio between the pulse's nonlinear frequency shift and the size of the topological band gap. Taking the weak spatial dispersion into account results then in the formation of stable edge quasi-solitons. Our findings are generic to systems governed by Dirac-like Hamiltonians and validated by numerical modeling of pulse propagation along a valley-Hall domain wall in staggered honeycomb waveguide lattices with Kerr nonlinearity.

physics.optics↗

arXiv2019

Locking and regularisation of chimeras by periodic forcing

We study how a chimera state in a one-dimensional medium of non-locally coupled oscillators responses to a periodic external force. On a macroscopic level, where chimera can be considered as an oscillating object, forcing leads to entrainment of the chimera's frequency inside an Arnold tongue. On a mesoscopic level, where chimera can be viewed as a inhomogeneous, stationary or nonstationary pattern, strong forcing can lead to reguralization of an unstationary chimera. On a microscopic level of the dynamics of individual oscillators, forcing outside of the Arnold tongue leads to a multi-plateu state with nontrivial locking properties.

nlin.PS↗

arXiv2016

Multipolar third-harmonic generation driven by optically-induced magnetic resonances

We analyze third-harmonic generation from high-index dielectric nanoparticles and discuss the basic features and multipolar nature of the parametrically generated electromagnetic fields near the Mie-type optical resonances. By combining both analytical and numerical methods, we study the nonlinear scattering from simple nanoparticle geometries such as spheres and disks in the vicinity of the magnetic dipole resonance. We reveal the approaches for manipulating and directing the resonantly enhanced nonlinear emission with subwavelength all-dielectric structures that can be of a particular interest for novel designs of nonlinear optical antennas and engineering the magnetic optical nonlinear response at nanoscale.

physics.optics↗

arXiv2014

Dissipative plasmon solitons in graphene nanodisk arrays

We study nonlinear modes in one-dimensional arrays of doped graphene nanodisks with Kerr-type nonlinear response in the presence of an external electric field. We present the theoretical model describing the evolution of the disks' polarizations, taking into account intrinsic graphene losses and dipole-dipole coupling between the graphene nanodisks. We reveal that this nonlinear system can support discrete dissipative scalar solitons of both longitudinal and transverse polarizations, as well as vector solitons composed of two mutually coupled polarization components. We demonstrate the formation of stable resting and moving localized modes under controlling guidance of the external driving field.

physics.optics↗

arXiv2014

Dynamics and stability of dark solitons in exciton-polariton condensates

We present a comprehensive analytical theory of localized nonlinear excitations - dark solitons, supported by an incoherently pumped, spatially homogeneous exciton-polariton condensate. We show that, in contrast to dark solitons in conservative systems, these nonlinear excitations "relax" by blending with the background at a finite time, which critically depends on the parameters of the condensate. Our analytical results for trajectory and lifetime are in excellent agreement with direct numerical simulations of the open-dissipative mean-field model. In addition, we show that transverse instability of quasi-one-dimensional dark stripes in a two-dimensional open-dissipative condensate demonstrates features that are entirely absent in conservative systems, as creation of vortex-antivortex pairs competes with the soliton relaxation process.

cond-mat.quant-gas↗