Non-Equilibrium Quantum Phases of Two-Atom Dicke Model

In this paper, we investigate the non-equilibrium quantum phases of the two-atom Dicke model, which can be realized in a two species Bose-Einstein condensate interacting with a single light mode in an optical cavity. Apart from the usual non-equilibrium normal and inverted phases, a non-equilibrium mixed phase is possible which is a combination of normal and inverted phase. A new kind of quantum phase transition is predicted from non-superradiant mixed phase to the superradiant phase which can be achieved by tuning the two different atom-photon couplings. We also show that a quantum phase transition from the non-superradiant mixed phase to the superradiant phase is forbidden for certain values of the two atom-photon coupling strengths.