We investigate the superfluid behavior of a Bose-Einstein condensate of ${}^6\mathrm{Li}$ 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 nonzero 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.

• Received 15 October 2015

DOI:https://doi.org/10.1103/PhysRevA.93.023634