Abstract
We present measurements of the critical velocity for vortex shedding in a highly oblate Bose-Einstein condensate with a moving repulsive Gaussian laser beam. As a function of the barrier height , the critical velocity shows a dip structure having a minimum at , where is the chemical potential of the condensate. At fixed , we observe that the ratio of to the speed of sound monotonically increases for decreasing , where is the beam width and is the condensate healing length. We explain our results with the density reduction effect of the soft boundary of the Gaussian obstacle, based on the local Landau criterion for superfluidity. The measured value of with our stiffest obstacle is about 0.4, which is in good agreement with theoretical predictions for a two-dimensional superflow past a circular cylinder.
- Received 12 February 2015
DOI:https://doi.org/10.1103/PhysRevA.91.053615
©2015 American Physical Society