Condensate fluctuations of interacting Bose gases within a microcanonical ensemble.

Based on counting statistics and Bogoliubov theory, we present a recurrence relation for the microcanonical partition function for a wealdy interacting Bose gas with a finite number of particles in a cubic box. According to this microcanonical partition function, we calculate numerically the distribution function, condensate fraction, and condensate fluctuations for a finite and isolated Bose-Einstein condensate. For ideal and weakly interacting Bose gases, we compare the condensate fluctuations with those in the canonical ensemble. The present approach yields an accurate account of the condensate fluctuations for temperatures close to the critical region. We emphasize that the interactions between excited atoms turn out to be important for moderate temperatures. [ABSTRACT FROM AUTHOR]