Coherence and clock shifts in ultracold Fermi gases with resonant interactions

TL;DR

This paper derives a general formula for rf line shifts in ultracold Fermi gases near resonances, revealing that shifts inversely depend on scattering length and explaining finite clock shifts at Feshbach resonances.

Contribution

It introduces a sum rule-based approach to relate rf line shifts to interaction parameters and correlation functions in ultracold Fermi gases.

Findings

Shifts vary inversely with scattering length near resonance.

Clock shifts remain finite at Feshbach resonances.

Theoretical results match experimental observations.

Abstract

Using arguments based on sum rules, we derive a general result for the average shifts of rf lines in Fermi gases in terms of interatomic interaction strengths and two-particle correlation functions. We show that near an interaction resonance shifts vary inversely with the atomic scattering length, rather than linearly as in dilute gases, thus accounting for the experimental observation that clock shifts remain finite at Feshbach resonances.