Bose-Einstein Condensate: A Superposition of Macroscopically Squeezed States

TL;DR

This paper investigates the ground state of a uniform Bose gas, revealing a superposition of macroscopically squeezed states that restores particle number conservation and exhibits normal fluctuations.

Contribution

It introduces a U(1) invariant ground state formed by superposing squeezed states, addressing particle number fluctuations in Bose-Einstein condensates.

Findings

Ground state obeys Hugenholtz-Pines theorem

Superposition restores particle number conservation

Fluctuations become normal in the new ground state

Abstract

We study the ground state of a uniform Bose gas at zero temperature in the Hartree-Fock-Bogoliubov (HFB) approximation. We find a solution of the HFB equations which obeys the Hugenholtz-Pines theorem. This solution imposes a macroscopic squeezing to the condensed state and as a consequence displays large particle number fluctuations. Particle number conservation is restored by building the appropriate U(1) invariant ground state via the superposition of the squeezed states. The condensed particle number distribution of this new ground state is calculated as well as its fluctuations which present a normal behavior.