Dynamics of thermalization of two tunnel-coupled one-dimensional quasicondensates

TL;DR

This paper investigates the non-equilibrium thermalization dynamics of two tunnel-coupled one-dimensional quasicondensates after a sudden change in coupling, revealing energy flow patterns and phase coherence evolution.

Contribution

It provides a detailed analysis of post-quench thermalization, including energy transfer mechanisms and phase coherence changes, in coupled quasicondensates with initial imbalances.

Findings

Energy can flow from colder to hotter quasicondensate under certain conditions.

Transient damped oscillations characterize the approach to equilibrium.

Phase coherence length can increase after thermalization despite higher temperature.

Abstract

We study the non-equilibrium dynamics of two tunnel-coupled one-dimensional quasicondensates following a quench of the coupling strength from zero to a fixed finite value. More specifically, starting from two independent quasicondensates in thermal equilibrium, with initial temperature and chemical potential imbalance, we suddenly switch on the tunnel-coupling and analyze the post-quench equilibration in terms of particle number and energy imbalances. We find that, in certain parameter regimes, the net energy can flow from the colder quasicondensate to the hotter one and is governed by the surplus of low energy particles flowing from the cold to the hot system relative to the high-energy particles flowing in the reverse direction. In all cases, the approach to the new thermal equilibrium occurs through transient, damped oscillations. We also find that for a balanced initial state the coupled quasicondensates can relax into a final thermal equilibrium state in which they display a thermal phase coherence length that is larger than their initial phase coherence length, even though the new equilibrium temperature is higher. The increase in the phase coherence length occurs due to phase locking which manifests itself via an increased degree of correlation between the local relative phases of the quasicondensates at two arbitrary points.