2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/135483A diffusion process is usually assumed for the phase of the order parameter of a Bose system of finite size. The theoretical basis is limited to the so called Bogoliubov approximation. We show that a suitable generalization of the Hartree-Fock-Bogoliubov approach recovers phase diffusion.Quantum Physicstext