Particle correlations in a fermi superfluid

TL;DR

This paper analyzes particle correlations in a superfluid Fermi gas, emphasizing the importance of conserving approximations and finite-momentum Cooper pairs, which are crucial for understanding the strongly correlated BCS-BEC crossover.

Contribution

It introduces a conserving approximation framework and incorporates finite-momentum Cooper pairs into the analysis of particle correlations.

Findings

Finite-momentum Cooper pairs significantly affect correlations.

Conserving approximation ensures particle number conservation.

Correlations reveal details of the BCS-BEC crossover.

Abstract

We discuss correlations between particles of different momentum in a superfluid fermi gas, accessible through noise measurements of absorption images of the expanded gas. We include two elements missing from the simplest treatment, based on the BCS wavefunction: the explicit use of a conserving approximation satisfying particle number conservation, and the inclusion of the contribution from Cooper pairs at finite momentum. We expect the latter to be a significant issue in the strongly correlated state emerging in the BCS-BEC crossover.