Extracting the condensate density from projection experiments with Fermi gases

TL;DR

This paper analyzes projection experiments in Fermi gases across the BCS-BEC crossover, linking measured condensate fractions to many-body correlations and providing theoretical insights into superfluid properties.

Contribution

It introduces a theoretical framework connecting projection experiment measurements to many-body correlations in the BCS-BEC crossover.

Findings

Identifies the quantum operator related to measured condensate fractions.

Relates projection measurements to many-body correlations.

Provides calculations across temperature and coupling ranges.

Abstract

A debated issue in the physics of the BCS-BEC crossover with trapped Fermi atoms is to identify characteristic properties of the superfluid phase. Recently, a condensate fraction was measured on the BCS side of the crossover by sweeping the system in a fast (nonadiabatic) way from the BCS to the BEC sides, thus ``projecting'' the initial many-body state onto a molecular condensate. We analyze here the theoretical implications of these projection experiments, by identifying the appropriate quantum-mechanical operator associated with the measured quantities and relating them to the many-body correlations occurring in the BCS-BEC crossover. Calculations are presented over wide temperature and coupling ranges, by including pairing fluctuations on top of mean field.