TO WHAT EXTENT THE SUPERFLUID 4 He IS SQUEEZED

Abstract

We show that the Bogoliubov microscopic theory of superuidity of liquid 4 He allows quantum uctuations of both condensate and excitations. Comparison of those uctuations leads to an equation determining the mean number of atoms with zero momentum in a self-consistent way. Obtained results are in good agreement with the experiments on Bose-Einstein condensation in atomic beams. To explain experimental results on low amount of atoms in condensate in the superuid phase of liquid 4 He, we propose to consider the ground state of the condensate as a squeezed number state and discuss some corollaries coming from this conjecture.