Probing superfluidity of Bose-Einstein condensates via laser stirring

TL;DR

This paper studies the superfluid properties of a Bose-Einstein condensate of $^6$Li molecules by analyzing how a laser stirrer affects heating rates, identifying the critical velocity and factors influencing it with strong experimental agreement.

Contribution

It provides a quantitative analysis of the critical velocity in a Bose-Einstein condensate, incorporating effects of temperature, stirrer motion, and density profile with both numerical and analytical methods.

Findings

Critical velocity is accurately predicted by the model.

Temperature and stirrer motion significantly affect superfluid behavior.

Model shows excellent agreement with experimental data.

Abstract

We investigate the superfluid behavior of a Bose-Einstein condensate of $^6$Li molecules. In the experiment by Weimer et al., Phys. Rev. Lett. 114, 095301 (2015) a condensate is stirred by a weak, red-detuned laser beam along a circular path around the trap center. The rate of induced heating increases steeply above a velocity $v_c$, which we define as the critical velocity. Below this velocity, the moving beam creates almost no heating. In this paper, we demonstrate a quantitative understanding of the critical velocity. Using both numerical and analytical methods, we identify the non-zero temperature, the circular motion of the stirrer, and the density profile of the cloud as key factors influencing the magnitude of $v_c$. A direct comparison to the experimental data shows excellent agreement.