Vortex shedding frequency of a moving obstacle in a Bose-Einstein condensate

Abstract

We experimentally investigate the periodic vortex shedding dynamics in a highly oblate Bose-Einstein condensate using a moving penetrable Gaussian obstacle. The shedding frequency $f_v$ is measured as a function of the obstacle velocity $v$ and characterized by a linear relationship of $f_v=a(v-v_c)$ with $v_c$ being the critical velocity. The proportionality constant $a$ is linearly decreased with a decrease in the obstacle strength, whereas $v_c$ approaches the speed of sound. When the obstacle size increases, both $a$ and $v_c$ are decreased. The critical vortex shedding is further investigated for an oscillating obstacle and found to be consistent with the measured $f_v$. When the obstacle's maximum velocity exceeds $v_c$ but its oscillation amplitude is not large enough to create a vortex dipole, we observe that vortices are generated in the low-density boundary region of the trapped condensate, which is attributed to the phonon emission from the oscillating obstacle. Finally, we discuss a possible asymptotic association of $a$ with the Strouhal number in the context of universal shedding dynamics of a superfluid.

9 pages, 6 figures

References in corpus (8)

• Superfluid behaviour of a two-dimensional Bose gas
• Relaxation of superfluid turbulence in highly oblate Bose-Einstein condensates
• Observation of von Kármán Vortex Street in an Atomic Superfluid Gas
• The critical velocity in the BEC-BCS crossover
• Identifying a superfluid Reynolds number via dynamical similarity
• Classical and quantum regimes of two-dimensional turbulence in trapped Bose-Einstein condensates
• Hysteresis in quantized vortex shedding
• Supersonic flow of a Bose-Einstein condensate past an oscillating attractive-repulsive obstacle

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• Proper Orthogonal Decomposition of a Superfluid Turbulent Wake
• Vortex shedding patterns in holographic superfluids at finite temperature