Engineering vortex rings and systems for controlled studies of vortex   interactions in Bose-Einstein condensates
  We study controlled methods of preparing vortex configurations in atomic Bose-Einstein condensates and their use in the studies of fundamental vortex scattering, reconnection processes and superfluid sound emission. We explore techniques of imprinting closed vortex rings by means of coherently driving internal atomic transitions with electromagnetic fields which exhibit singular phase profiles. In particular, we show that a vortex ring can be prepared in a controlled way by two focused co-propagating Gaussian laser beams. More complex vortex systems may also be imprinted by directly superposing simpler field configurations or by programming their phase profiles on optical holograms. This provides the controlled method of studying vortex reconnections in atomic superfluids. We analyze specific examples of two merging vortex rings in a trapped two-component Rb-87 condensate. We calculate the radiated sound energy in the vortex ring reconnection process and show that the vortex relaxation and the re-distribution of sound energy can be controlled by the imprinting process. The energy is first concentrated towards the trap center and later emitted outwards as sound and transformed to surface excitations. As another such technique, we study creating pairs of 2D point vortices in Bose-Einstein condensates using a 'light roadblock' in ultra-slow light propagation. We show how this can be used to study vortex collisions in compressible superfluids and how these collisions result in energy dissipation via phonons and, sometimes, annihilation of vortex pairs. 
J. Ruostekoski and Z. Dutton