arXiv subjects

A. I. Pavlov

Publications and source records attributed to A. I. Pavlov.

9 recordsLinked to original sources

arXiv2025

Dynamic thermalization on noisy quantum hardware

Emulating thermal observables on a digital quantum computer is essential for quantum simulation of many-body physics. However, thermalization typically requires a large system size due to incorporating a thermal bath, whilst limited resources of near-term digital quantum processors allow for simulating relatively small systems. We show that thermal observables and fluctuations may be obtained for a small closed system without a thermal bath. Thermal observables occur upon classically averaging quantum mechanical observables over randomized variants of their time evolution that run independently on a digital quantum processor. Using an IBM quantum computer, we experimentally find thermal occupation probabilities with finite positive and negative temperatures defined by the initial state's energy. Averaging over random evolutions facilitates error mitigation, with the noise contributing to the temperature in the simulated observables. This result fosters probing the dynamical emergence of equilibrium properties of matter at finite temperatures on noisy intermediate-scale quantum hardware.

quant-ph↗

arXiv2023

Ultrafast dynamics of cold Fermi gas after a local quench

We consider non-equilibrium dynamics of two initially independent reservoirs $A$ and $B$ filled with a cold Fermi gas coupled and decoupled by two quantum quenches following one another. We find that the von Neumann entropy production induced by the quench is faster than thermal transport between the reservoirs and defines the short-time dynamics of the system. We analyze the energy change in the system which adds up the heat transferred between $A$ and $B$ and the work done by the quench to uncouple the reservoirs. In the case when $A$ and $B$ interact for a short time, we notice an energy increase in both reservoirs upon decoupling. This energy gain results from the quench's work and does not depend on the initial temperature imbalance between the reservoirs. We relate the quench's work to the mutual correlations of $A$ and $B$ expressed through their von Neumann entropies. Utilizing this relation, we show that once $A$ and $B$ become coupled, their entropies grow (on a timescale of the Fermi time) faster than the heat flow within the system. This result may provide a track of quantum correlations' generation at finite temperatures which one may probe in ultracold atoms, where we expect the characteristic timescale of correlations' growth to be $\sim 0.1 {\rm ms}$.

cond-mat.quant-gas↗

arXiv2022

Energy dynamics, information and heat flow in quenched cooling and the crossover from quantum to classical thermodynamics

The dynamics when a hot many-body quantum system is brought into instantaneous contact with a cold many-body quantum system can be understood as a combination of early time quantum correlation (von Neumann entropy) gain and late time energy relaxation. We show that at the shortest timescales there is an energy increase in each system linked to the entropy gain, even though equilibrium thermodynamics does not apply. This energy increase is of quantum origin and results from the collective binding energy between the two systems. Counter-intuitively, this implies that also the hotter of the two systems generically experiences an initial energy increase when brought into contact with the other colder system. In the limit where the energy relaxation overwhelms the (quantum) correlation build-up, classical energy dynamics emerges where the energy in the hot system decreases immediately upon contact with a cooler system. We use both strongly correlated SYK systems and weakly correlated mixed field Ising chains to exhibit these characteristics, and comment on its implications for both black hole evaporation and quantum thermodynamics.

hep-th↗

arXiv2021

Quantum tunneling dynamics in a complex-valued Sachdev-Ye-Kitaev model quench-coupled to a cool bath

The Sachdev-Ye-Kitaev (SYK) model describes interacting fermionic zero modes in zero spatial dimensions, e.g. quantum dot, with interactions strong enough to completely washout quasiparticle excitations in the infrared. In this paper, we consider the complex-valued SYK model at initial temperature $T$ and chemical potential $μ$ coupled to a large reservoir by a quench at time $t=0$. The reservoir is kept at zero temperature and charge neutrality. We find that the dynamics of the discharging process of the SYK quantum dot reveals a distinctive characteristic of the SYK non-Fermi liquid (nFl) state. In particular, we focus on the tunneling current induced by the quench. We show that the temperature dependent contribution to the current's half-life scales linearly in $T$ at low temperatures for the SYK nFl state, while for the Fermi liquid it scales as $T^2$.

cond-mat.str-el↗

arXiv2020

Planckian superconductor

The Planckian relaxation rate $\hbar/t_\mathrm{P} = 2πk_\mathrm{B} T$ sets a characteristic time scale for both equilibration of quantum critical systems and maximal quantum chaos. In this note, we show that at the critical coupling between a superconducting dot and the complex Sachdev-Ye-Kitaev model, known to be maximally chaotic, the pairing gap $Δ$ behaves as $η\,\, \hbar/t_\mathrm{P}$ at low temperatures, where $η$ is an order one constant. The lower critical temperature emerges with a further increase of the coupling strength so that the finite $Δ$ domain is settled between the two critical temperatures.

cond-mat.str-el↗

arXiv2016

The influence of boundary conditions on the form of the optical beam in the array of coupled optical waveguides

We investigate the optical beam behavior in the periodical array of the coupled optical waveguides with the monotonic change of the refractive index in the transverse direction. We consider the dependence of the form of the optical beam on the boundary conditions. It is well known that if the input wave packet is wide enough, the optical Bloch oscillations occur, while for the enough narrow input wave packet the breathing mode is observed. We show that if the input wave packet is neither too wide nor too narrow, the optical beam takes a peculiar form which can be considered neither as the Bloch oscillations nor as the breathing mode. We qualitatively explain the transformation of this intermediate form of the optical beam when the width of the input wave packet changes.

cond-mat.mes-hall↗

arXiv2015

Anharmonic Bloch Oscillations in the Optical Waveguide Array

The anharmonic Bloch oscillations of a light beam in the array of optical waveguides are considered. The coupling modes model (CMM) with the second order interaction is used to describe the effect analytically. The formula obtained predicts explicitly the path of the optical beam, in particular, the positions of the turning points are found. A total agreement of this formula with the numerical simulation is confirmed.

cond-mat.mes-hall↗

arXiv2014

Electron-Hole Liquid in the Couple Quantum Wells

It is shown that the homogeneous state of the spatially separated electrons and holes in the coupled quantum wells (CQW) is instable if the layer charge density is smaller than the critical value specified by the parameters of the CQW. The effect is due to the many-body Coulomb correlations which provide the positive compressibility. The instability results in the formation of the inhomogeneous system which comprises the liquid electron-hole drops.

cond-mat.mes-hall↗

arXiv2000

Cosmic Ray Air Shower Characteristics in the Framework of the Parton-Based Gribov-Regge Model NEXUS

The purpose of this paper is twofold: first we want to introduce a new type of hadronic interaction model (NEXUS), which has a much more solid theoretical basis as, for example, presently used models like QGSJET and VENUS, and ensures therefore a much more reliable extrapolation towards high energies. Secondly, we want to promote an extensive air shower (EAS) calculation scheme, based on cascade equations rather than explicit Monte Carlo simulations, which is very accurate in calculations of main EAS characteristics and extremely fast concerning computing time. We employ the NEXUS model to provide the necessary data on particle production in hadron-air collisions and present the average EAS characteristics for energies 10^14 - 10^17 eV. The experimental data of the casa-blanka group are analyzed in the framework of the new model.

hep-ph↗