Nonlinear Atom-Photon Interaction Induced Population Inversion and Inverted Quantum Phase Transition of Bose-Einstein Condensate in an Optical Cavity

摘要

In this paper we explore the rich structure of macroscopic many-particlequantum states for Bose- Einstein condensate in an optical cavity with thetunable nonlinear atom-photon interaction [Nature (London) 464, 1301 (2010)].Population inversion, bistable normal phases and the coexistence ofnormal{superradiant phases are revealed by adjusting of the experimentallyrealizable interaction strength and pump-laser frequency. For the negative(effective) cavity-frequency we observe remark- ably an inverted quantum phasetransition (QPT) from the superradiant to normal phases with the increase ofatom-field coupling, which is just opposite to the QPT in the normal Dickemodel. The bistable macroscopic states are derived analytically in terms of thespin-coherent-state variational method by taking into account of both normaland inverted pseudospin states.