Vortex cluster shedding in an oblate Bose-Einstein condensate

We present the observation of vortex cluster shedding from a moving obstacle in an oblate Bose-Einstein condensate (BEC). We investigate the evolution of the vortex shedding pattern as a function of the obstacle velocity v, and observe regular shedding of vortex clusters consisting of two like-sign vortices at low obstacle velocity. As v increases, the vortex shedding pattern becomes irregular with many larger clusters, which shows a transition to turbulence. To quantitatively characterize the vortex shedding pattern, we analyze the cluster charge distribution as a function of the obstacle velocity. The transition from regular to turbulent shedding is manifested with a rapid decrease of fractional population of two like-sign vortex clusters. In particular, we observe a saturating behavior of the Stouhal number with increasing v, which is associated with the shedding frequency. We will discuss possible extension of this work to test the universality of the vortex shedding dynamics.