Ground-state properties of a Bose-Einstein condensate in an optomechanical cavity

Abstract

In this paper, we investigate the ground-state properties of a Bose-Einstein condensate in an optomechanical cavity, in which a nonlinear photon-phonon interaction is created through the radiation pressure. We find that this nonlinear photon-phonon interaction can enhance the macroscopic collective excitations, and more importantly, it can generate a phase, called the dynamical unstable phase, in a regime of strong interaction. Moreover, the transition from the superradiant phase to the dynamical unstable phase shows no breaking of symmetry but is an intrinsic transition governed only by the ground-state stability. The possible physical explanation is also illustrated. These predictions can be detected by measuring the atom population, the mean photon number, or the mean phonon number in experiments.