Damping-free collective oscillations of a driven two-component Bose gas   in optical lattices
  We explore quantum many-body physics of a driven Bose-Einstein condensate in optical lattices. The laser field induces a gap in the generalized Bogoliubov spectrum proportional to the effective Rabi frequency. The lowest lying modes in a driven condensate are characterized by zero group velocity and non-zero current. Thus, the laser field induces roton modes, which carry interaction in a driven condensate. We show that collective excitations below the energy of the laser-induced gap remain undamped, while above the gap they are characterized by a significantly suppressed Landau damping rate. 
Gavriil Shchedrin, Daniel Jaschke, and Lincoln D. Carr
cond-mat.quant-gas quant-ph