Light-shift-induced quantum phase transitions of a Bose-Einstein   condensate in the optical cavities
  In this paper we reveal the rich ground-state properties induced by the strong nonlinear atom-photon interaction, which has been found in the recent experiment about a Bose-Einstein condensate coupling with a high-finesse cavity [Nature (London) 464, 1301 (2010)]. Two detuning-dependent phase diagrams are revealed by investigating the experimentally-measurable atomic population. In particular, two new quantum phase transitions from the superradiant phase or the normal phase to a dynamically-unstable phase are predicted in the blue detuning, and moreover, the three-phase coexistence points are found. It is also demonstrated that these predicted quantum phase transitions are the intrinsic transitions governed only by the second-order derivative of the ground-state energy. Finally, we also point out that the region involving coexistence of the superradiant phase and the normal phase predicted before can not happen in the ground state. 
Ni Liu, Jinling Lian, Jie Ma, Liantuan Xiao, Gang Chen, J. -Q. Liang,   and Suotang Jia
quant-ph cond-mat.quant-gas