title: Observation of von Kármán Vortex Street in an Atomic Superfluid Gas.
abstract: We report on the experimental observation of vortex cluster shedding from a moving obstacle in an oblate atomic Bose-Einstein condensate. At low obstacle velocities v above a critical value, vortex clusters consisting of two like-sign vortices are generated to form a regular configuration like a von Kármán street, and as v is increased, the shedding pattern becomes irregular with many different kinds of vortex clusters. In particular, we observe that the Stouhal number associated with the shedding frequency exhibits saturation behavior with increasing v. The regular-to-turbulent transition of the vortex cluster shedding reveals remarkable similarities between a superfluid and a classical viscous fluid. Our work opens a new direction for experimental investigations of the superfluid Reynolds number characterizing universal superfluid hydrodynamics.
authors.affiliation: Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea.
authors.forename: Woo Jin
authors.initials: WJ
authors.lastname: Kwon
authors.affiliation: Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea.|Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea.
authors.forename: Joon Hyun
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea.
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Seo
authors.affiliation: Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea.|Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea.
authors.forename: Y
authors.initials: Y
authors.lastname: Shin