Molecular Probe of Pairing in the BEC-BCS Crossover

TL;DR

This paper uses optical spectroscopy to investigate pairing in ultracold lithium atoms across the BEC-BCS crossover, providing evidence for pairing and supporting the universality of broad Feshbach resonances.

Contribution

It introduces a novel optical molecular spectroscopy method to measure the closed-channel contribution and pairing dynamics in the BEC-BCS crossover.

Findings

Small closed-channel contribution supports universality.

Clear evidence of pairing across the crossover.

Method enables precise measurement of pairing dynamics.

Abstract

We have used optical molecular spectroscopy to probe the many-body state of paired $^6$Li atoms near a broad Feshbach resonance. The optical probe projects pairs of atoms onto a vibrational level of an excited molecule. The rate of excitation enables a precise measurement of the closed-channel contribution to the paired state. This contribution is found to be quite small, supporting the concept of universality for the description of broad Feshbach resonances. The dynamics of the excitation provide clear evidence for pairing across the BEC-BCS crossover, and into the weakly interacting BCS regime.