Green's function method to the ground state properties of a two-component Bose-Einstein condensate

The elementary excitation spectrum of a two-component Bose-Einstein condensate is obtained by Green's function method. It is found to have two branches. In the long-wave limit, the two branches of the excitation spectrum are reduced to one phonon excitation and one single-particle excitation. With the obtained excitation spectrum and the Green's functions, the depletion of the condensate and the ground state energy have also been calculated in this paper. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3633685]