arXiv subjects

Nikolay Yegovtsev

Publications and source records attributed to Nikolay Yegovtsev.

10 recordsLinked to original sources

arXiv2026

Topological chirality of dissipative limit cycles in an open Dicke model

In an open, $U(1)$-symmetric Dicke model with chiral atom-cavity couplings, we show that dissipation drives two limit-cycle phases of opposite chirality in the thermodynamic limit, obtaining exact analytical solutions. These phases are separated by a $U(1)$-broken superradiant state, lending the phase diagram a topological character, and persist under $U(1)$-preserving perturbations, making them candidates for chiral continuous time crystals. In addition to stable normal and inverted steady states, the model also exhibits multistability, where the long-time dynamics is set by the initial state. Our results establish dissipation as a resource for inducing chiral dynamical order in light-matter coupled systems.

cond-mat.quant-gas↗

arXiv2026

Robust continuous symmetry breaking and multiversality in the chiral Dicke model

The Dicke model (DM) serves as a paradigm for understanding collective light-matter interactions. We introduce the chiral Dicke model, a generalization where an atomic ensemble couples to a two-mode cavity via chiral interactions. Unlike the standard DM, the chiral DM is endowed with an inherent continuous $U(1)$ symmetry associated with angular momentum conservation. The ground-state phase diagram and the associated quantum phase transitions are charted out, revealing a $U(1)$-broken superradiant phase that spans a broad parameter space. We demonstrate that the spectrum of quantum fluctuations is highly tunable in both the symmetric and broken phases. Strikingly, our calculations reveal that the system exhibits `multiversality', where distinct universality classes govern the transition between the same two phases. In particular, along a special line in parameter space, the dynamical critical exponent for the normal-superradiant phase transition changes from $zν=1$ to $zν=1/2$. Our work establishes the chiral Dicke model as a powerful platform to realize novel quantum phases and multiversal critical phenomena in light-matter coupled systems.

quant-ph↗

arXiv2025

Unified theory of attractive and repulsive polarons in one-dimensional Bose gas

We present a unified description of attractive and repulsive polarons, formed in a one-dimensional Bose gas hosting an impurity particle, by obtaining all ground and excited state solutions to the Gross-Pitaevskii equation. Modeling the impurity with an attractive square-well potential, we characterize the excited-state energy branches as a function of interaction strength. As the impurity-bath coupling increases, the excited states change from distinct soliton configurations to hybridized soliton-polaron states, eventually crossing over from repulsive to attractive polarons at unitarity. We identify a universal regime near this crossover where the polaron properties are accurately characterized by the zero-energy scattering length.

cond-mat.quant-gas↗

arXiv2025

Heavy Fermi polarons in a one-dimensional harmonic trap

We provide an analytically tractable toy model of an infinitely heavy impurity interacting with the spin-polarized gas of bath fermions via a contact potential in 1D and placed in a harmonic trap. The solution to this problem requires knowledge of the single-particle fermionic eigenstates in the presence of a harmonic trap and a contact potential. We show how the spectrum can be understood from a perturbative solution of the exact transcendental equation in the weak and strong-coupling regimes. We additionally provide expressions for normalized wavefunctions and different overlaps between the states in the presence and absence of the impurity. Using these exact results, we analyze the energy of the polaron, derive Tan's contact-like relation for the density at the center of the harmonic trap, and compute the quasiparticle residue.

cond-mat.quant-gas↗

arXiv2025

Fermi polarons with the finite-range fermion-impurity interactions

We study a problem of an infinitely heavy impurity introduced into a polarized Fermi gas, which can be solved exactly with the help of Fumi's theorem. We consider the regime of finite-range fermion-impurity interactions beyond the standard $s$-wave scattering regime and investigate how this affects the energy of the polaron. We show how one can account for the effective range effects as well as the contribution from higher angular momentum channels, which are important for the study of ionic and Rydberg polarons. Our findings have relevance for atomic gas mixtures with a large mass imbalance and for the impurities trapped inside the optical tweezers.

cond-mat.quant-gas↗

arXiv2024

Exact results for heavy unitary Bose polarons

We consider the problem of unitary Bose polarons, i.e., impurities interacting via a potential with infinite scattering length with a bath of weakly interacting bosons. We provide an analytic expression for the energy of a heavy impurity whose interaction potential has a range larger than the healing length of the bath. Furthermore, we perform numerically exact Diffusion Monte Carlo calculations and we demonstrate that the simple Gross-Pitaevskii theory provides a remarkably accurate description of heavy unitary Bose polarons throughout the whole experimentally relevant range of gas densities.

cond-mat.quant-gas↗

arXiv2023

Effective mass and interaction energy of heavy Bose polarons at unitarity

We study the motion of a heavy impurity immersed in a weakly interacting BEC using the Gross-Pitaevskii equation (GPe). We construct a perturbative solution to the GPe in powers of impurity velocity in the case when the boson-impurity potential is tuned to unitarity and calculate the effective mass of the polaron. In addition, we calculate the interaction energy of two unitary polarons which are sufficiently far apart. Our formalism also reproduces the results for both the mass and interaction energy obtained at weak boson-impurity coupling.

cond-mat.quant-gas↗

arXiv2022

Strongly interacting impurities in a dilute Bose condensate

An impurity in a Bose gas is commonly referred to as Bose polaron. For a dilute Bose gas its properties are expected to be universal, that is dependent only on a few parameters characterizing the boson-impurity interactions. When boson-impurity interactions are weak, it has been known for some time that the properties of the polaron depend only on the scattering length of these interactions. In this paper which accompanies and extends Ref. [Phys. Rev. Lett. 126, 123403 (2021)] (where some of these results have already been reported) we examine stronger boson-impurity interactions, keeping their range finite. We demonstrate that for attractive interactions between impurity and the bosons up to and including the unitary point of these interactions, all static properties of a Bose polaron in a dilute Bose gas can be calculated in terms of the scattering length and an additional parameter which characterizes the range of the impurity-boson interactions. We show that our approach to this problem is valid if this parameter does not deviate too much from the scattering length of intra-boson interactions, with the precise criterion given in the text. We produce explicit expressions for the energy and other properties of polaron for the case when the impurity-boson scattering length is tuned to unitarity, and we also provide the first correction away from it.

cond-mat.quant-gas↗

arXiv2020

Universal aspects of a strongly interacting impurity in a dilute Bose condensate

We study the properties of an impurity immersed in a weakly interacting Bose gas, i.e., of a Bose polaron. In the perturbatively-tractable of limit weak impurity-boson interactions many of its properties are known to depend only on the scattering length. Here we demonstrate that for strong (unitary) impurity-boson interactions all static quasiproperties of a Bose polaron in a dilute Bose gas, such as its energy, its residue, its Tan's contact and the number of bosons trapped nearby the impurity, depend on the impurity-boson potential via a single parameter.

cond-mat.quant-gas↗

arXiv2019

Dynamical quantum phase transitions in many-body localized systems

We investigate dynamical quantum phase transitions in disordered quantum many-body models that can support many-body localized phases. Employing $l$-bits formalism, we lay out the conditions for which singularities indicative of the transitions appear in the context of many-body localization. Using the combination of the mapping onto $l$-bits and exact diagonalization results, we explicitly demonstrate the presence of these singularities for a candidate model that features many-body localization. Our work paves the way for understanding dynamical quantum phase transitions in the context of many-body localization, and elucidating whether different phases of the latter can be detected from analyzing the former. The results presented are experimentally accessible with state-of-the-art ultracold-atom and ion-trap setups.

cond-mat.stat-mech↗