arXiv subjects

Alexander Yakimenko

Publications and source records attributed to Alexander Yakimenko.

At least 19 recordsLinked to original sources

arXiv2026

Josephson spectroscopy in a circular atomic tunnel junction with acceleration-induced symmetry breaking

We study Josephson dynamics in a long atomic Bose-Josephson junction formed by two tunnel-coupled coplanar Bose-Einstein-condensate rings. An in-plane linear acceleration breaks the axial symmetry of the trap and transforms a single Josephson plasma oscillation into a multimode population-imbalance response. Gross-Pitaevskii simulations and Bogoliubov-de Gennes analysis show that the additional spectral components arise from collective modes that acquire finite overlap with the population-imbalance operator under symmetry breaking, with their activation governed by reflection symmetry about the acceleration direction. We also propose a mode-resolved Josephson-spectroscopy protocol based on a weak localized periodic perturbation. Frequency scans reveal resonant amplitude peaks and phase shifts at the eigenfrequencies of active Bogoliubov modes, while angular scans of the drive position provide access to the angular structure of the corresponding mode density perturbations. A dissipative time-dependent Bogoliubov theory yields analytical response functions in quantitative agreement with full Gross-Pitaevskii simulations in the linear regime. Our results demonstrate that accelerated dual-ring condensates provide a controllable platform for symmetry-selected Josephson dynamics and spectroscopic probing of collective modes.

cond-mat.quant-gas↗

arXiv2026

Dynamics of repeated BEC formation and extraction in dimple traps

We investigate repeated Bose-Einstein-condensate (BEC) formation and extraction in a dimple trap embedded in a reservoir of thermal atoms using a kinetic model. The model includes pulsed extraction, evaporation, three-body losses, and thermal-atom replenishment. Three extraction protocols are compared: extraction of all atoms from the dimple (BEC and thermal atoms), full and partial extractions of the BEC, but not of the thermal atoms. Residual atoms in the dimple after extraction seed subsequent Bose-stimulated growth and reduce the recovery time between extractions, but also enhance density-dependent losses. For all protocols, repeated extraction of BECs can be achieved without replenishment, but the number of BEC formations is limited by reservoir depletion and heating. With continuous replenishment, the system can reach a periodic steady-state regime, after an initial transient period, controlled by the externally imposed rates of extraction pulses and thermal-atom input. Within the explored parameter range, partial BEC extraction gives the highest efficiency, particularly for short extraction periods and high input rates. These results identify seeding by residual populations of BECs and thermal atoms as a kinetic mechanism for improving repeated condensate production in dimple traps.

cond-mat.quant-gas↗

arXiv2026

Collective dynamics of active matter with orientation-weighted alignment

We study an agent-based model of self-propelled particles with a velocity-dependent alignment rule. This interaction is orientation weighted and acts along the line connecting neighboring particles. Tuning the alignment strength produces several distinct collective regimes, including disordered gas-like motion, coherent flocking, jammed high-density states, and densely ordered moving clusters with active-crystal-like behavior. These results show that a simple local alignment rule can generate a broad range of nonequilibrium collective dynamics within a single microscopic model.

cond-mat.soft↗

arXiv2025

Hawking-radiation-ignited autocatalytic formation of primordial black holes

We propose and analyze an autocatalytic mechanism in which bursts of Hawking radiation from evaporating micro-primordial black holes (PBHs) trigger the collapse of near-critical plasma overdensities. In a primordial plasma seeded with such patches, this feedback self organizes into a traveling ignition front that successively forms new PBHs and then self-quenches as the Universe expands. A minimal reaction-diffusion model yields conservative criteria for ignition and freeze-out and predicts a stochastic gravitational-wave background with a sharp causal low-frequency edge set by the freeze-out correlation length and largely insensitive to Planck-scale PBH endpoint microphysics. The resulting sub-Hz-to-audio band and amplitudes satisfy cosmological energy-injection bounds, providing a clean, testable target for forthcoming gravitational-wave observatories.

gr-qc↗

arXiv2025

Emergent momentum-space topological pseudospin defects in non-Hermitian systems

Topological defects are central to modern physics, from spintronics to photonics, due to their robustness and potential application in information processing. In this work, we discuss topological point defects that spontaneously emerge at the imaginary Fermi arcs (degeneracy lines) in momentum space of two-dimensional systems described by non-Hermitian effective Hamiltonians. In particular, we consider a generic non-Hermitian Dirac model and a phenomenological model describing hybrid light-matter quasiparticles - exciton polaritons hosted in an optical microcavity. In both cases, the eigenenergies of the system have both real and imaginary parts and form two distinct bands corresponding to two (pseudo-)spin states. We describe the trajectories of the point defects characterized by integer-valued topological winding (vorticity) analytically and show that the defects with opposite vorticity annihilate with each other in the fully gapped phases, but are protected from annihilation by the non-Hermitian spectral degeneracies (exceptional and hybrid points) in the gapless phases. We also suggest that the signatures of these defects can be experimentally measured in an exciton-polariton system.

cond-mat.mes-hall↗

arXiv2025

Solitons in Quasiperiodic Lattices with Fractional Diffraction

We study the dynamics of solitons under the action of one-dimensional quasiperiodic lattice potentials, fractional diffraction, and nonlinearity. The formation and stability of the solitons is investigated in the framework of the fractional nonlinear Schrödinger equation. By means of variational and numerical methods, we identify conditions under which stable solitons emerge, stressing the effect of the fractional diffraction on soliton properties. The reported findings contribute to the understanding of the soliton behavior in complex media, with implications for topological photonics and matter-wave dynamics in lattice potentials.

nlin.PS↗

arXiv2025

Collective Excitations of Self-Gravitating Ultralight Dark Matter Cores

A distinctive feature of ultralight bosonic dark matter is its ability to form a Bose-Einstein condensate with a dense, stationary configuration at the center of galactic halos. In this work, we investigate the internal dynamics of such cores by numerically solving the Bogoliubov-de Gennes equations within a fully self-consistent gravitational framework, accounting for both gravitational potential perturbations and local self-interactions. We demonstrate that the solitonic core supports a discrete spectrum of well-defined collective modes. These oscillations characterize the linear response of the core to perturbations and may influence various dynamical processes. We also discuss potential astrophysical implications of these excitations on galactic scales.

astro-ph.CO↗

arXiv2024

Acceleration-driven dynamics of Josephson vortices in coplanar superfluid rings

Precise control of topologically protected excitations, such as quantum vortices in atomtronic circuits, opens new possibilities for future quantum technologies. We theoretically investigate the dynamics of Josephson vortices (rotational fluxons) induced by coupled persistent currents in a system of coplanar double-ring atomic Bose-Einstein condensates. We study the Josephson effect in an atomic Josephson junction formed by coaxial ring-shaped condensates. Tunneling superflows, initiated by an imbalance in atomic populations between the rings, are significantly influenced by the persistent currents in the inner and outer rings. This results in pronounced Josephson oscillations in the population imbalance for both co-rotating and non-rotating states. If a linear acceleration is applied to the system, our analysis reveals peculiar azimuthal tunneling patterns and dynamics of Josephson vortices which leads to non-zero net tunneling current and shows sensitivity to the acceleration magnitude. When multiple Josephson vortices are present, asymmetric vortex displacements that correlate with both the magnitude and direction of acceleration can be measured, offering potential for quantum sensing applications.

cond-mat.quant-gas↗

arXiv2023

Acoustic Analogues of Extremal Rotating Black Holes in Exciton-Polariton Condensates

We theoretically investigate the acoustic analogues of high-angular-momentum rotating black holes in exciton-polariton condensates. Performing numerical simulations of a long-lived ring-shaped condensate configuration with an acoustic horizon and ergoregion for high angular momentum states, we observed a quasi-stable state near critical angular momentum where the acoustic black hole horizon disappears. Our findings offer an insight into the quantum nature of the instability of naked singularity.

cond-mat.quant-gas↗

arXiv2023

Engineering phase and density of Bose-Einstein condensates in curved waveguides with toroidal topology

We investigate the effects of ellipticity-induced curvature on atomic Bose-Einstein condensates confined in quasi-one-dimensional closed-loop waveguides. Our theoretical study reveals intriguing phenomena arising from the interplay between curvature and interactions. Density modulations are observed in regions of high curvature, but these modulations are suppressed by strong repulsive interactions. Additionally, we observe phase accumulation in regions with the lowest curvature when the waveguide with persistent current is squeezed. Furthermore, waveguides hosting persistent currents exhibit dynamic transformations between states with different angular momenta. These findings provide insights into the behavior of atomic condensates in curved waveguides, with implications for fundamental physics and quantum technologies. The interplay between curvature and interactions offers opportunities for exploring novel quantum phenomena and engineering quantum states in confined geometries.

cond-mat.quant-gas↗

arXiv2023

Making ghost vortices visible in two-component Bose-Einstein condensates

Ghost vortices constitute an elusive class of topological excitations in quantum fluids since the relevant phase singularities fall within regions where the superfluid density is almost zero. Here we present a platform that allows for the controlled generation and observation of such vortices. Upon rotating an imbalanced mixture of two-component Bose-Einstein condensates (BECs), one can obtain necklaces of real vortices in the majority component whose cores get filled by particles from the minority one. The wavefunction describing the state of the latter is shown to harbour a number of ghost vortices which are crucial to support the overall dynamics of the mixture. Their arrangement typically mirrors that of their real counterpart, hence resulting in a ``dual" ghost-vortex necklace, whose properties are thoroughly investigated in the present paper. We also present a viable experimental protocol for the direct observation of ghost vortices in a ${}^{23}\mathrm{Na}$ $+$ ${}^{39}\mathrm{K}$ ultracold mixture. Quenching the inter-component scattering length, some atoms are expelled from the vortex cores and, while diffusing, swirl around unpopulated phase singularities, thus turning them directly observable.

cond-mat.quant-gas↗

arXiv2022

Generation of Josephson vortices in stacked toroidal Bose-Einstein condensates

Coupled coaxially stacked toroidal condensates with persistent currents suggest an appealing physical platform for the investigation of various phenomena related to interacting superflows from Josephson effects in the regime of weak interactions to the quantum Kelvin-Helmholtz instability for merging rings. We suggest experimentally accessible methods to prepare states with different topological charges in two coupled coaxial ring-shaped atomic Bose-Einstein condensates. Our results open up the way to direct observation of rotational Josephson vortices in atomic Bose-Einstein condensates.

cond-mat.quant-gas↗

arXiv2020

Acoustic analogue of Hawking radiation in quantized circular superflows of Bose-Einstein condensates

We propose emulation of Hawking radiation (HR) by means of acoustic excitations propagating on top of persistent current in an atomic Bose-Einstein condensate (BEC) loaded in an annular confining potential. The setting is initially created as a spatially uniform one, and then switches into a nonuniform configuration, while maintaining uniform BEC density. The eventual setting admits the realization of sonic black and white event horizons with different slopes of the local sound speed. A smooth slope near the white-hole horizon suppresses instabilities in the supersonic region. It is found that tongue-shaped patterns of the density-density correlation function, which represent the acoustic analog of HR, are strongly affected by the radius of the ring-shaped configuration and number of discrete acoustic modes admitted by it. There is a minimum radius that enables the emulation of HR. We also briefly discuss a possible similarity of properties of the matter-wave sonic black holes to the known puzzle of the stability of Planck-scale primordial black holes in quantum gravity.

cond-mat.quant-gas↗

arXiv2019

Nonlinear dynamics of Josephson vortices in merging superfluid rings

We consider merger of two parallel toroidal atomic Bose-Einstein condensates with different vorticities in a three-dimensional (3D) trap. In the tunnel-coupling regime, Josephson vortices (rotational fluxons) emerge in the barrier between the superflows. When the barrier is gradually eliminated, we observe essentially three-dimensional evolution of quantum vortices, which may include the development of the Kelvin-Helmholtz instability at the interface between the rings, in the framework of a weakly dissipative Gross-Pitaevskii equation. An initially more populated ring, carrying a persistent current, can drag an initially non-rotating less populated one into the same vortex state. The final state of the condensate crucially depends on an initial population imbalance in the double-ring set, as well as on the shape of the 3D trapping potential, oblate or prolate. In the prolate (axially elongated) configuration, robust 3D hybrid structures may appear as a result of the merger of persistent currents corresponding to different vorticities.

cond-mat.quant-gas↗

arXiv2019

Symmetry breaking in interacting ring-shaped superflows of Bose-Einstein condensates

We demonstrate that the evolution of superflows in interacting persistent currents of ultracold gases is strongly affected by symmetry breaking of the quantum vortex dynamics. We study counter-propagating superflows in a system of two parallel rings in regimes of weak (a Josephson junction with tunneling through the barrier) and strong (rings merging across a reduced barrier) interactions. For the weakly interacting toroidal Bose-Einstein condensates, formation of rotational fluxons (Josephson vortices) is associated with spontaneous breaking of the rotational symmetry of the tunneling superflows. The influence of a controllable symmetry breaking on the final state of the merging counter-propagating superflows is investigated in the framework of a weakly dissipative mean-field model. It is demonstrated that the population imbalance between the merging flows and the breaking of the underlying rotational symmetry can drive the double-ring system to final states with different angular momenta.

cond-mat.quant-gas↗

arXiv2019

Tunneling of persistent currents in coupled ring-shaped Bose-Einstein condensates

Considerable progress in experimental studies of atomic gases in a toroidal geometry has opened up novel prospects for the investigation of fundamental properties of superfluid states and creation of new configurations for atomtronic circuits. In particular, atomic Bose-Einstein condensates loaded in a dual-ring trap suggest a possibility to consider the tunneling dynamics between coupled condensates with different angular momenta. Accordingly, we address the tunneling in a pair of coaxial ring-shaped condensates separated by a horizontal potential barrier. A weak-coupling truncated (finite-mode) Galerkin model and direct numerical simulations of the underlying three-dimensional Gross-Pitaevskii equation are used for the analysis of tunneling superflows driven by an initial imbalance in atomic populations of the rings. The superflows through the Bose-Josephson junction are strongly affected by persistent currents which are present in the rings. Josephson oscillations of the population imbalance and angular momenta in the coupled rings are obtained for co-rotating states and non-rotating ones. On the other hand, the azimuthal structure of the tunneling flow implies formation of Josephson vortices (fluxons) with zero net current through the junction for hybrid states, built of counter-rotating persistent currents in the coupled rings.

cond-mat.quant-gas↗

arXiv2016

Stochastic phase slips in toroidal Bose-Einstein condensates

Motivated by recent experiments we study the influence of thermal noise on the phase slips in toroidal Bose-Einstein condensates with a rotating weak link. We derive a generalized Arrhenius-like expression for the rate of stochastic phase slips. We develop a method to estimate the energy barrier separating different superflow states. The parameters at which the energy barrier disappears agree with the critical parameters for deterministic phase slips obtained from dynamics simulations, which confirms the validity of our energetic analysis. We reveal that adding thermal noise lowers the phase-slip threshold. However, the quantitative impact of the stochastic phase slips turns out to be too small to explain the significant discrepancy between theoretical and the experimental results.

cond-mat.quant-gas↗

arXiv2014

Stability of persistent currents in open-dissipative quantum fluids

The phenomenon of stable persistent currents is central to the studies of superfluidity in a range of physical systems. While all of the previous theoretical studies of superfluid flows in annular geometries concentrated on conservative systems, here we extend the stability analysis of persistent currents to open-dissipative exciton-polariton superfluids. By considering an exciton-polariton condensate in an optically-induced annular trap, we determine stability conditions for an initially imposed flow with a non-zero orbital angular momentum. We show, theoretically and numerically, that the system can sustain metastable persistent currents in a large parameter region, and describe scenarios of the supercurrent decay due to the dynamical instability.

cond-mat.quant-gas↗