Observations on Sound Propagation in Rapidly Rotating Bose-Einstein   Condensates
  Repulsive laser potential pulses applied to vortex lattices of rapidly rotating Bose-Einstein condensates create propagating density waves which we have observed experimentally and modeled computationally to high accuracy. We have observed a rich variety of dynamical phenomena ranging from interference effects and shock-wave formation to anisotropic sound propagation. 
T.P. Simula, P. Engels, I. Coddington, V. Schweikhard, E.A. Cornell,   and R.J. Ballagh