Crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas

TL;DR

This paper demonstrates a reversible adiabatic crossover from a molecular Bose-Einstein condensate to a degenerate Fermi gas of lithium atoms, observing a smooth size change and strong interactions indicative of superfluidity.

Contribution

It provides experimental evidence of a reversible, adiabatic crossover between molecular BEC and Fermi gas, with high condensate fraction and in situ imaging of the process.

Findings

Cloud size changes smoothly across the crossover

Strong interactions observed at Feshbach resonance

High condensate fraction suggests superfluidity

Abstract

We demonstrate a reversible conversion of a Li2 molecular Bose-Einstein condensate to a degenerate Fermi gas of atoms by adiabatically crossing a Feshbach resonance. By optical in situ imaging, we observe a smooth change of the cloud size in the crossover regime. On the Feshbach resonance, the ensemble is strongly interacting and the measured cloud size is 75(7)% of the one of a non-interacting zero-temperature Fermi gas. The high condensate fraction of more than 90% and the adiabatic crossover suggest our Fermi gas to be cold enough to form a superfluid.