High temperature expansion applied to fermions near Feshbach resonance

TL;DR

This paper demonstrates that many properties of a degenerate Fermi gas near a Feshbach resonance persist at high temperatures, showing universal behavior and reversible molecule formation without a phase transition.

Contribution

It applies high temperature expansion to fermions near Feshbach resonance, revealing universal properties and behavior in the Boltzmann regime that mirror low-temperature phenomena.

Findings

Feshbach resonance unshifted at high temperatures

Reversible formation of molecules by sweeping across the resonance

Interaction energy remains negative and continuous

Abstract

We show that, apart from a difference in scale, all of the surprising recently observed properties of a degenerate Fermi gas near a Feshbach resonance persist in the high temperature Boltzmann regime. In this regime, the Feshbach resonance is unshifted. By sweeping across the resonance, a thermal distribution of bound states (molecules) can be reversibly generated. Throughout this process, the interaction energy is negative and continuous. We also show that this behavior must persist at lower temperatures unless there is a phase transition as the temperature is lowered. We rigorously demonstrate universal behavior near the resonance.