Periodic shedding of vortex dipoles from a moving penetrable obstacle in a Bose-Einstein condensate

Abstract

We investigate vortex shedding from a moving penetrable obstacle in a highly oblate Bose-Einstein condensate. The penetrable obstacle is formed by a repulsive Gaussian laser beam that has the potential barrier height lower than the chemical potential of the condensate. The moving obstacle periodically generates vortex dipoles and the vortex shedding frequency fv linearly increases with the obstacle velocity v as fv = a(v − vc), where vc is a critical velocity. Based on periodic shedding behavior, we demonstrate deterministic generation of a single vortex dipole by applying a short linear sweep of a laser beam. This method will allow further controlled vortex experiments such as dipole-dipole collisions.

Vortices and vortex lattices in quantum ferrofluids

“…• Motion of a localized obstacle or potential (as generated by a tightly-focussed blue-detuned laser beam) through a condensate (or, equivalently, motion of the condensate relative to a static obstacle) leads to the nucleation of vortices above a critical relative speed [37,38,142], forming a quantum wake downstream of the obstacle. The critical speed is related to the Landau criterion which predicts the formation of elementary excitations in the fluid for relative speeds exceeding…”

“…(38) Substituting into the dipolar GPE (5) an equation for the amplitude f about the vortex is obtained,…”

“…Vortical structures have been generated experimentally in non-dipolar condensates in the form of single vortices [35,36], vortex-antivortex pairs [37,38], vortex rings [39] and vortex lattices [40,41], as well as disordered vortex distributions characteristic of quantum turbulence [42][43][44]. These excitations underpin a variety of rich phenomena, including vortex lattices, quantum turbulence, the Berezinskii-Kosterlitz-Thouless transition and Kibble-Zurek defect formation.…”

Superfluids Hit the Street

“…Would the superfluid show universal behavior in the wake response to a moving obstacle, and can we define a proper Reynolds number Re s characterizing it [2][3][4][5]? It has been clearly demonstrated that a superfluid becomes dissipative via quantum vortex emission when the obstacle velocity exceeds a critical velocity v c [6][7][8][9][10][11][12][13]. Since turbulent flow would be generated by strong perturbations of the obstacle at significantly high v, the key issue is whether regular vortex shedding like the von Kármán street occurs in an intermediate v regime.…”

“…[11][12][13]. We prepare a highly oblate BEC of 23 Na atoms in a harmonic trapping potential which is generated by combining a pancake-shaped optical dipole trap and a magnetic quadruple trap.…”