Observation of Spin Superfluidity in a Bose Gas Mixture

TL;DR

This paper experimentally demonstrates spin superfluidity in a Bose-Einstein condensate mixture of sodium atoms, revealing frictionless counterflow and spin drag effects at finite temperature.

Contribution

First experimental observation of spin superfluidity in a Bose gas mixture, including analysis of collisional and collisionless regimes and measurement of polarizability.

Findings

Counter flow oscillations without friction in condensates

Damped thermal component motion due to spin drag

Large increase in condensate polarizability at finite temperature

Abstract

The spin dynamics of a harmonically trapped Bose-Einstein condensed binary mixture of sodium atoms is experimentally investigated at finite temperature. In the collisional regime the motion of the thermal component is shown to be damped because of spin drag, while the two condensates exhibit a counter flow oscillation without friction, thereby providing direct evidence for spin superfluidity. Results are also reported in the collisionless regime where the spin components of both the condensate and thermal part oscillate without damping, their relative motion being driven by a mean field effect. We also measure the static polarizability of the condensed and thermal parts and we find a large increase of the condensate polarizability with respect to the T=0 value, in agreement with the predictions of theory.