Green’s Function Theory on A Fluctuation of Condensed Particle Number in Bose-Einstein Condensed Systems

Abstract

By using the Green’s function theory, we studied the fluctuation of condensed particle number for Bose-Einstein condensed systems in the canonical ensemble. The expressions for the fluctuations can be expressed by the Green’s functions.  Our results are consistent with previous theories in Bogoliubov approximation. In addition, a single-particle and a pair condensation equally contribute to the mean-square fluctuation of the condensates.