Observation of a Strongly-Interacting Degenerate Fermi Gas of Atoms

TL;DR

This paper reports the experimental observation of a strongly-interacting, degenerate Fermi gas of $^6$Li atoms, revealing complex expansion behavior indicative of superfluidity or collisional hydrodynamics.

Contribution

First observation of a highly-degenerate, strongly-interacting Fermi gas of atoms with detailed analysis of its expansion dynamics.

Findings

Rapid transverse expansion upon release from trap

Evidence suggesting superfluid behavior in the gas

Inadequacy of collisional hydrodynamics to explain data

Abstract

We report on the observation of a highly-degenerate, strongly-interacting Fermi gas of atoms. Fermionic $^6$Li atoms in an optical trap are evaporatively cooled to degeneracy using a magnetic field to induce strong, resonant interactions. Upon abruptly releasing the cloud from the trap, the gas is observed to expand rapidly in the transverse direction while remaining nearly stationary in the axial. We interpret the expansion dynamics in terms of collisionless superfluid and collisional hydrodynamics. For the data taken at the longest evaporation times, we find that collisional hydrodynamics does not provide a satisfactory explanation, while superfluidity is plausible.