Inflationary quasiparticle creation and thermalization dynamics in coupled Bose-Einstein condensates

TL;DR

This paper studies how quasiparticles are created and how the system thermalizes in a coupled Bose-Einstein condensate, revealing avalanche-like creation and a slow relaxation to a thermal state influenced by initial conditions.

Contribution

It introduces a detailed dynamical analysis of quasiparticle creation and thermalization in a non-equilibrium BEC system using Keldysh-Bogoliubov equations, highlighting a resonance-driven avalanche process.

Findings

Avalanche-like quasiparticle creation due to parametric resonance.

Slow exponential relaxation to a thermal state.

BEC acts as a grand canonical reservoir for quasiparticles.

Abstract

A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, non-equilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanche-like QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our set-up occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.