Observation of a Strongly-Interacting Degenerate Fermi Gas of Atoms

TL;DR

For the data taken at the longest evaporation times, it is found that collisional hydrodynamics does not provide a satisfactory explanation, whereas superfluidity is plausible.

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.

Figures (3)

• Figure 1: False-color absorption images of a strongly interacting, degenerate Fermi gas as a function of time $t$ after release from full trap depth for $t=0.1-2.0$ ms, top to bottom. The axial width of the gas remains nearly stationary as the transverse width expands rapidly.
• Figure 2: One-dimensional spatial distributions in the transverse ( A) and axial ( B) directions (red, 0.4 ms; blue, 1.0 ms; green, 2.0 ms). The transverse distributions are shown fit with zero-temperature Thomas-Fermi distributions, while the axial are shown fit with gaussian distributions.
• Figure 3: ( A) Transverse (red) and axial (blue) widths as functions of time after release. The solid curves are theoretical predictions based on hydrodynamic scaling with no free parameters. ( B) Aspect ratio of the cloud as a function of time after release. The dots indicate experimental data and the solid curves show theoretical predictions with no adjustable parameters (red, hydrodynamic; blue, ballistic; green, attractive mean field; orange, repulsive mean field).