ABSTRACT
In the ideal Bose gas, a finite fraction of the particles occupy the same singleparticle state below a critical temperature, forming a Bose-Einstein condensate. When the particles have mutual interactions, however, single-particle states are no longer meaningful. Nevertheless, we can still define a condensate wave function ψ(r), as the quantum amplitude for removing a particle from the condensate at position r. Its complex conjugate ψ∗(r) is the amplitude for creating a particle.
