FLUCTUATIONS OF THE PARTICLE NUMBER IN A TRAPPED BOSE-EINSTEIN CONDENSATE

We develop a reliable procedure for calculating the microcanonical flu ctuations of the ground state occupation number for harmonically trapp ed ideal Bose gases, and show that these fluctuations vanish uniformly when the temperature approaches zero. The key point is the precise de termination of the number of microstates from the canonical partition sum, thus avoiding a failure of the usual saddle point method. We also demonstrate why the magnitude of the condensate fluctuations does not depend on the total particle number. [S0031-9007(97)04478-5].