Johannes Kombe, Jean-Sébastien Bernier, Michael Köhl, and Corinna Kollath:
Phys. Rev. A 100, 013604 (2019)
We investigate the nonequilibrium behavior of dilute, attractively interacting Fermi gases subjected to finite-duration ramps of their internal interaction strength. We identify three dynamical regimes as a function of ramp duration using a time-dependent version of the Bardeen-Cooper-Schrieffer theory of superconductivity to model these systems. For short ramp durations, these systems become nonsuperconducting; however, fermions with opposite momenta remain paired albeit with reduced amplitudes, and the associated pair amplitude distribution is nonthermal. In this first regime, the disappearance of superconductivity is due to the loss of phase coherence between pairs. By contrast, for intermediate ramp durations, superconductivity survives but the magnitude of the order parameter is reduced and presents long-lived oscillations. Finally, for long ramp durations, phase coherence is almost fully retained during the finite-duration interaction quench, and the steady state is characterized by a thermal-like pair amplitude distribution. Using this approach, one can therefore dynamically tune the coherence between pairs to control the magnitude of the superconducting order parameter and even engineer a nonequilibrium state made of preformed pairs.