Phase Separation and Dynamics of two-component Bose-Einstein condensates

TL;DR

This paper investigates the phase separation and dynamics of two-component Bose-Einstein condensates, revealing how damping rates and oscillation frequencies can map the phase diagram in trapped gases using a self-consistent finite-temperature kinetic theory.

Contribution

It introduces a new method to determine the phase boundary in trapped two-component condensates by analyzing oscillation damping rates and frequencies, beyond the traditional miscibility parameter.

Findings

Damping rates differ between miscible and immiscible regimes.

Surface oscillations and counterflow instabilities explain damping behavior.

Atom numbers critically influence phase boundary location.

Abstract

The miscibility of two interacting quantum systems is an important testing ground for the understanding of complex quantum systems. Two-component Bose-Einstein condensates enable the investigation of this scenario in a particularly well controlled setting. In a homogeneous system, the transition between mixed and separated phases is fully characterised by a `miscibility parameter', based on the ratio of intra- to inter-species interaction strengths. Here we show, however, that this parameter is no longer the optimal one for trapped gases, for which the location of the phase boundary depends critically on atom numbers. We demonstrate how monitoring of damping rates and frequencies of dipole oscillations enables the experimental mapping of the phase diagram by numerical implementation of a fully self-consistent finite-temperature kinetic theory for binary condensates. The change in damping rate is explained in terms of surface oscillation in the immiscible regime, and counterflow instability in the miscible regime, with collisions becoming only important in the long time evolution.