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.
Highlights
Bose-Einstein condensates (BECs) are attractive systems for studying the nonequilibrium dynamics of interacting quantum gases [1]
We find that the mean-field interactions between the BECs and the thermal clouds are by far the dominant damping mechanisms; inclusion of collisions appears essential at long time scales ( γ −1) to eliminate residual center-of-mass oscillations, as evident by the 39K centers of mass (COMs) oscillations shown in the bottom panels of Fig. 4
We have provided numerical evidence that for a trapped condensate mixture with overlapping trap centers, the miscible-immiscible transition depends critically on the condensate numbers, deviating from the simple homogeneous prediction used to date. We demonstrate that this transition can be mapped out experimentally by measuring the damping rate and the frequency of the dipole oscillations, the predominant contribution to which stems from mean-field coupling
Summary
Bose-Einstein condensates (BECs) are attractive systems for studying the nonequilibrium dynamics of interacting quantum gases [1]. The aim of this article is fourfold: (i) to demonstrate that for a trapped binary mixture, = 0 is generally no longer the optimal criterion for the transition boundary; (ii) to characterize the full phase diagram (see Fig. 1) based on the identification of a new parameter; (iii) to propose measurements of the frequency and damping rates of induced dipole oscillations as a universal experimental tool for mapping out the phase diagram; and (iv) to demonstrate the importance of thermal effects on the dynamics, by providing a numerical implementation of a fully self-consistent finite-temperature model for binary mixtures [37] This extends the successful Zaremba-Nikuni-Griffin (ZNG) model [38] to two components.
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