Coherence and Clock Shifts in Ultracold Fermi Gases with Resonant Interactions

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.

Figure 1

Correlation function $\partial (E/N)/\partial a_{12}^{-1}$ in units of $p_F/2m$ calculated from the data of Ref. 6.

Figure 2

Calculated clock shift for a gas of ${}^6\mathrm{Li}$ atoms at zero temperature as a function of magnetic field. See the text for details.