COHERENT-STATE TREATMENT OF NONEQUILIBRIUM BOSE CONDENSATION
非平衡玻色凝结的相干态处理

Based on the mean field and Bogoliubov approximations, we linearize the Hamiltonian of a nonequilibrium Bose condensed system, which is created by an external coherent pump field, and coupled to a reservoir. It is found that the dynamical algebra of the linearized Hamiltonian is Heisenberg and SU(1,1) Lie algebra if the coupling to reservoir is not taken into account. By using the methods of coherent state, we obtain its eigenvalues and eigen-functions-direct product of displaced squeezed-number-states and generalized SU(1,1) coherent states. Then we introduce the retarded Green's functions of elementary excitations to calculate its spectrum in the coupling situation, and further give the state functions of exciton system in weakly coupling situation.