A Non-Equilibrium Kinetic Theory for Trapped Binary Condensates

TL;DR

This paper develops a non-equilibrium kinetic theory for binary Bose-Einstein condensates, analyzing collisional processes and hydrodynamic behavior to guide experimental studies of ultracold atomic mixtures.

Contribution

It introduces a coupled set of dissipative Gross-Pitaevskii and Quantum Boltzmann equations for binary condensates, identifying eight collisional processes affecting equilibration.

Findings

Numerical analysis of collisional rates in Rb-K mixtures.

Assessment of hydrodynamic regime accessibility in experiments.

Characterization of trap geometry effects on system dynamics.

Abstract

We derive a non-equilibrium finite-temperature kinetic theory for a binary mixture of two interacting atomic Bose-Einstein condensates and use it to explore the degree of hydrodynamicity attainable in realistic experimental geometries. Based on the standard separation of timescale argument of kinetic theory, the dynamics of the condensates of the multi-component system are shown to be described by dissipative Gross-Pitaevskii equations, self-consistently coupled to corresponding Quantum Boltzmann equations for the non-condensate atoms: on top of the usual mean field contributions, our scheme identifies a total of eight distinct collisional processes, whose dynamical interplay is expected to be responsible for the systems equilibration. In order to provide their first characterization, we perform a detailed numerical analysis of the role of trap frequency and geometry on collisional rates for experimentally accessible mixtures of $^{87}$Rb-$^{41}$K and $^{87}$Rb-$^{85}$Rb, discussing the extent to which the system may approach the hydrodynamic regime with regard to some of those processes, as a guide for future experimental investigations of ultracold Bose gas mixtures.