Nonequilibrium Dynamics and Thermodynamics of a Degenerate Fermi Gas Across a Feshbach Resonance

We consider a two-species degenerate Fermi gas coupled by a diatomic Feshbach resonance. We show that the resulting superfluid can exhibit a form of coherent BEC-to-BCS oscillations in response to a nonadiabatic change in the system’s parameters, such as, for example, a sudden shift in the position of the Feshbach resonance. In the narrow resonance limit, the resulting solitonlike collisionless dynamics can be calculated analytically. In equilibrium, the thermodynamics can be accurately computed across the full range of BCS-BEC crossover, with corrections controlled by the ratio of the resonance width to the Fermi energy.

Figure 1

Atomic momentum distribution $n_p$ displaying oscillations between a Fermi sea and Bose-condensed molecules. The atomic depletion in $n_p$ of width $\Delta \approx \gamma \sqrt{{\omega }_0}$ appears at the molecular energy determined by the detuning ${\omega }_0$.