Quantum Phase Transition in Ultracold 87Rb Atom Gas with Radiant Field

A second-order quantum phase transition in two-species Bose-Einstein condensates of 87Rb atoms coupled by a quantized radiant field is revealed explicitly in terms of the energy spectrum which is obtained in the thermodynamic limit and is controllable by the coupling parameter between the atom and field. The scaling behavior of the collective excitation modes at the critical transition point is seen to be in the same universality class as that of the Dicke model. It is also demonstrated that the quantum phase transition is realizable below the critical temperature of BEC and can be detected experimentally by measuring the abrupt change of atom population imbalance.