Exploring the BEC-BCS Crossover with an Ultracold Gas of $^6$Li Atoms

TL;DR

This paper reports on experiments with ultracold $^6$Li atoms to explore the transition from Bose-Einstein condensation to BCS superfluidity, demonstrating superfluidity through various measurements across interaction regimes.

Contribution

It provides comprehensive experimental characterization of the BEC-BCS crossover in ultracold Fermi gases using Feshbach resonances, including measurements of interaction energy, collective modes, and pairing gap.

Findings

Observation of superfluidity in strongly interacting Fermi gas

Measurement of pairing gap across the crossover

Characterization of collective excitation modes

Abstract

We present an overview of our recent measurements on the crossover from a Bose-Einstein condensate of molecules to a Bardeen-Cooper-Schrieffer superfluid. The experiments are performed on a two-component spin-mixture of $^6$Li atoms, where a Fesh\-bach resonance serves as the experimental key to tune the s-wave scattering length and thus to explore the various interaction regimes. In the BEC-BCS crossover, we have characterized the interaction energy by measuring the size of the trapped gas, we have studied collective excitation modes, and we have observed the pairing gap. Our observations provide strong evidence for superfluidity in the strongly interacting Fermi gas.