Annihilation of vortex dipoles in an Oblate Bose-Einstein Condensate
  We theoretically explore the annihilation of vortex dipoles, generated when an obstacle moves through an oblate Bose-Einstein condensate, and examine the energetics of the annihilation event. We show that the gray soliton, which results from the vortex dipole annihilation, is lower in energy than the vortex dipole. We also investigate the annihilation events numerically and observe that the annihilation occurs only when the vortex dipole overtakes the obstacle and comes closer than the coherence length. Furthermore, we find that the noise reduces the probability of annihilation events. This may explain the lack of annihilation events in experimental realizations. 
Shashi Prabhakar, R. P. Singh, S. Gautam and D. Angom
physics.atm-clus cond-mat.quant-gas physics.optics