arXiv subjects

A. Kamenev

Publications and source records attributed to A. Kamenev.

At least 19 recordsLinked to original sources

arXiv2026

Large Fluctuations in Open Quantum Systems

We study statistics of atypical measurement outcomes in the steady states of driven open quantum systems. In equilibrium, the probability distribution over the phase space, as encoded in, e.g., the Wigner function, is analytic in the phase-space coordinates. We show that this property is generically lost in driven dissipative systems: their {\it large-deviation function} develops lines and surfaces across which its derivatives are discontinuous. As an illustrative example, we consider a parametrically driven Kerr oscillator coupled linearly and/or nonlinearly to a dissipative bath. Rare fluctuations in the amplitude and phase of the induced oscillations are governed by semiclassical instanton trajectories of the corresponding Keldysh-Lindblad action. We demonstrate that a given fluctuation can be realized through multiple distinct instanton trajectories. The competition between these trajectories leads to abrupt switching of the dominant instanton and, consequently, to non-analytic features in the large-deviation function.

quant-ph↗

arXiv2018

On the replica structure of Sachdev-Ye-Kitaev model

We investigate existence of replica off-diagonal solutions in the field-theoretical description of Sachdev-Ye-Kitaev model. To this end we evaluate a set of local and non-local dynamic correlation functions in the long time limit. We argue that the structure of the soft-mode Schwarzian action is qualitatively different in replica-diagonal vs. replica-off-diagonal scenarios, leading to distinct long-time predictions for the correlation functions. We then evaluate the corresponding correlation functions numerically and compare the simulations with analytical predictions of replica-diagonal and replica-off-diagonal calculations. We conclude that all our numerical results are in a quantitative agreement with the theory based on the replica-diagonal saddle point plus Schwarzian and massive Gaussian fluctuations (the latter do contain replica off-diagonal components). This seems to exclude any contributions from replica-off-diagonal saddle points, at least on the time scales shorter than the inverse many-body level spacing.

hep-th↗

arXiv2011

Dynamics of nano-magnetic oscillators

We explore how non-equilibrium noise affects spin-torque switching elements and oscillators. To do so we first discuss the deterministic dynamics of magnetic tunnel junctions, introducing a convenient set of slow and fast degrees of freedom. We then derive effective Langevin equation for the slowly varying energy of precessional orbit and introduce the corresponding energy noise and energy diffusion coefficient. This allows for the formulation of a Fokker-Planck equation for the energy density distribution. We use it to analyse switching time distribution as well as the shape of the optimal spin-current pulse, which minimizes Joule losses of a switch. Finally we derive a generic expression for the linewidth of a spin-torque oscillator and discuss its dependence on temperature, spin-current amplitude and other parameters.

cond-mat.mes-hall↗

arXiv2011

Doublon relaxation in the Bose-Hubbard model

Decay of a high-energy double occupancy state, doublon, in a narrow-band lattice requires creation of a coherent many-particle excitation. This leads to an exponentially long relaxation time of such a state. We show that, if the average occupation number is sufficiently small, the corresponding exponent may be evaluated exactly. To this end we develop the quasiclassical approach to calculation of the high-order tree-level decay amplitudes.

cond-mat.quant-gas↗

arXiv2010

Spin Torque Dynamics with Noise in Magnetic Nano-System

We investigate the role of equilibrium and nonequilibrium noise in the magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic model we present a detailed derivation of the spin shot noise correlator. We investigate the ramifications of the nonequilibrium noise on the spin torque dynamics, both in the steady state precessional regime and the spin switching regime. In the latter case we apply a generalized Fokker-Planck approach to spin switching, which models the switching by an Arrhenius law with an effective elevated temperature. We calculate the renormalization of the effective temperature due to spin shot noise and show that the nonequilibrium noise leads to the creation of cold and hot spot with respect to the noise intensity.

cond-mat.mes-hall↗

arXiv2010

Quantum decay of dark solitons in one dimensional Bose systems

Unless protected by the exact integrability, solitons are subject to dissipative forces, originating from a thermally fluctuating background. At low enough temperatures $T$ background fluctuations should be considered as being quantized which enables us to calculate finite lifetime of the solitons $τ\sim T^{-4}$. We also find that the coherent nature of the quantum fluctuations leads to long-range interactions between the solitons mediated by the superradiation. Our results are of relevance to current experiments with ultracold atoms, while the approach may be extended to solitons in other media.

cond-mat.quant-gas↗

arXiv2009

Dynamics of a one-dimensional spinor Bose liquid: a phenomenological approach

The ground state of a spinor Bose liquid is ferromagnetic, while the softest excitation above the ground state is the magnon mode. The dispersion relation of the magnon in a one-dimensional liquid is periodic in the wavenumber q with the period 2πn, determined by the density n of the liquid. Dynamic correlation functions, such as e.g. spin-spin correlation function, exhibit power-law singularities at the magnon spectrum, $ω\toω_m(q,n)$. Without using any specific model of the inter-particle interactions, we relate the corresponding exponents to independently measurable quantities $\partialω_m/\partial q$ and $\partialω_m/\partial n$.

cond-mat.mes-hall↗

arXiv2009

Bloch oscillations in one-dimensional spinor gas

A force applied to a spin-flipped particle in a one-dimensional spinor gas may lead to Bloch oscillations of particle's position and velocity. The existence of Bloch oscillations crucially depends on the viscous friction force exerted by the rest of the gas on the spin excitation. We evaluate the friction in terms of the quantum fluid parameters. In particular, we show that the friction is absent for integrable cases, such as SU(2) symmetric gas of bosons or fermions. For small deviations from the exact integrability the friction is very weak, opening the possibility to observe Bloch oscillations.

cond-mat.stat-mech↗

arXiv2008

Photo-Solitonic Effect

We show that dark solitons in 1D Bose liquids may be created by absorption of a single quanta of an external ac field, in a close analogy with the Einstein's photoelectric effect. Similarly to the von Lenard's experiment with photoexcited electrons, the external field's photon energy $\hbarω$ should exceed a certain threshold. In our case the latter is given by the soliton energy $\varepsilon_s(\hbar q)$ with the momentum $\hbar q$, where $q$ is photon's wavenumber. We find the probability of soliton creation to have a power-law dependence on the frequency detuning $ω-\varepsilon_s/\hbar$. This dependence is a signature of the quantum nature of the absorption process and the orthogonality catastrophe phenomenon associated with it.

cond-mat.other↗

arXiv2008

Spin-torque shot noise in magnetic tunnel junctions

Spin polarized current may transfer angular momentum to a ferromagnet, resulting in a spin-torque phenomenon. At the same time the shot noise, associated with the current, leads to a non-equilibrium stochastic force acting on the ferromagnet. We derive stochastic version of Landau-Lifshitz-Gilbert equation for a magnetization of a ''free'' ferromagnetic layer in contact with a ''fixed'' ferromagnet. We solve the corresponding Fokker-Planck equation and show that the non-equilibrium noise yields to a non-monotonous dependence of the precession spectrum linewidth on the current.

cond-mat.mes-hall↗

arXiv2007

Generating dark solitons by single photons

We show that dark solitons in 1D bose systems may be excited by resonant absorption of single quanta of an external ac field. The energy of the quantum $\hbarω$ should be slightly blue-detuned from the energy of a soliton with momentum $\hbar q$, where $q$ is the external field wavenumber $q$. We calculate the absorption cross-section and show that it has power-law dependence on the frequency detuning. This reflects the quantum nature of the absorption process and the orthogonality catastrophe phenomenon associated with it.

cond-mat.other↗

arXiv2007

Fermi-Luttinger liquid: Spectral function of interacting one-dimensional fermions

We evaluate the spectral function of interacting fermions in one dimension. Contrary to the Tomonaga-Luttinger model, our treatment accounts for the nonlinearity of the free fermion spectrum. In a striking departure from the Luttinger liquid theory, the spectrum nonlinearity restores the main feature of the Fermi liquid: a Lorentzian peak in the spectral function on the particle mass-shell. At the same time, the spectral function displays a power-law singularity on the hole mass-shell, similar to that in the Luttinger liquid.

cond-mat.mes-hall↗

arXiv2007

Dynamics of excitations in a one-dimensional Bose liquid

We show that the dynamic structure factor of a one-dimensional Bose liquid has a power-law singularity defining the main mode of collective excitations. Using the Lieb-Liniger model, we evaluate the corresponding exponent as a function of the wave vector and the interaction strength.

cond-mat.stat-mech↗

arXiv2006

Dynamic response of one-dimensional interacting fermions

We evaluate the dynamic structure factor $S(q,ω)$ of interacting one-dimensional spinless fermions with a nonlinear dispersion relation. The combined effect of the nonlinear dispersion and of the interactions leads to new universal features of $S(q,ω)$. The sharp peak $S\propto qδ(ω-uq)$, characteristic for the Tomonaga-Luttinger model, broadens up; $S(q,ω)$ for a fixed $q$ becomes finite at arbitrarily large $ω$. The main spectral weight, however, is confined to a narrow frequency interval of the width $δω\sim q^2/m$. At the boundaries of this interval the structure factor exhibits power-law singularities with exponents depending on the interaction strength and on the wave number $q$.

cond-mat.mes-hall↗

arXiv2005

Ion exchange phase transitions in "doped" water--filled channels

Ion transport through narrow water--filled channels is impeded by a high electrostatic barrier. The latter originates from the large ratio of the dielectric constants of the water and a surrounding media. We show that ``doping'', i.e. immobile charges attached to the walls of the channel, substantially reduces the barrier. This explains why most of the biological ion channels are ``doped''. We show that at rather generic conditions the channels may undergo ion exchange phase transitions (typically of the first order). Upon such a transition a finite latent concentration of ions may either enter or leave the channel, or be exchanged between the ions of different valences. We discuss possible implications of these transitions for the Ca-vs.-Na selectivity of biological Ca channels. We also show that transport of divalent Ca ions is assisted by their fractionalization into two separate excitations.

cond-mat.soft↗

arXiv2005

Conductance of ion channels and nanopores with charged walls: a toy model

We consider ion transport through protein ion channels in lipid membranes and water-filled nanopores in silicon films. It is known that, due to the large ratio of dielectric constants of water and the surrounding material, an ion placed inside the channel faces a large electrostatic self-energy barrier. The barrier leads to an exponentially large resistance of the channel. We study reduction of the electrostatic barrier by immobile charges located on the internal walls of the channel. We show that the barrier practically vanishes already at relatively small concentration of wall charges.

cond-mat.soft↗

arXiv2005

Transport in one dimensional Coulomb gases: From ion channels to nanopores

We consider a class of systems where, due to the large mismatch of dielectric constants, the Coulomb interaction is approximately one-dimensional. Examples include ion channels in lipid membranes and water filled nanopores in silicon or cellulose acetate films. Charge transport across such systems possesses the activation behavior associated with the large electrostatic self-energy of a charge placed inside the channel. We show here that the activation barrier exhibits non-trivial dependence on the salt concentration in the surrounding water solution and on the length and radius of the channel.

cond-mat.stat-mech↗

arXiv2004

Ehrenfest time in the weak dynamical localization

The quantum kicked rotor (QKR) is known to exhibit dynamical localization in the space of its angular momentum. The present paper is devoted to the systematic first--principal (without a regularizer) diagrammatic calculations of the weak--localization corrections for QKR. Our particular emphasis is on the Ehrenfest time regime -- the phenomena characteristic for the classical--to--quantum crossover of classically chaotic systems.

cond-mat.mes-hall↗