Superfluidity in sympathetic cooling with atomic Bose condensates

TL;DR

This paper demonstrates that superfluidity in atomic Bose-Einstein condensates restricts impurity scattering to velocities above the sound speed, offering a new way to detect superfluidity and suggesting $^{6}$Li as a candidate for sympathetic cooling.

Contribution

It reveals the superfluidity-induced velocity threshold for impurity scattering and proposes $^{6}$Li as a suitable impurity for sympathetic cooling with sodium condensates.

Findings

Impurity atoms are not scattered if their velocity is below the condensate sound velocity.

Superfluidity limits cooling efficiency for impurity velocities below $c$.

$^{6}$Li can be effectively cooled using a $^{23}$Na condensate.

Abstract

The dynamical structure of an atomic Bose-Einstein condensate limits the efficiency of the condensate in cooling slow impurity atoms. To illustrate the point, we show that an impurity atom moving in a homogeneous zero-temperature condensate is not scattered incoherently if its velocity is lower than the condensate sound velocity $c$, limiting cooling to velocities $v \geq c$. This striking effect is an expression of superfluidity and provides a direct means to detect the fundamental property of superfluidity in atomic condensates. Furthermore, we show that the fermionic lithium-isotope, $^{6}$Li, is a reasonable candidate for sympathetic cooling by a $^{23}$Na-condensate.