  We consider a homogeneous Bose gas of particles with an attractive
interaction. Mean field theory predicts for this system a spontaneous symmetry
breaking at a certain value of the interaction strength. We show that at this
point a second-order quantum phase transition occurs. We investigate the system
in the vicinity of the critical point using Bogoliubov theory and a continuous
description, that allows us to analyze {\it quantum fluctuations} in the system
even when the Bogoliubov approach breaks down.
