Solitons and Rabi Oscillations in a Time-Dependent BCS Pairing Problem

Abstract

Motivated by recent efforts to achieve cold fermions pairing near a Feshbach resonance, we consider the dynamics of formation of the Bardeen-Cooper-Schrieffer (BCS) state. At times shorter than the quasiparticle energy relaxation time, after the interaction is turned on, the dynamics of the system is nondissipative. We show that this collective nonlinear evolution of the BCS-Bogoliubov amplitudes (u,v) along with the pairing function, is an integrable dynamical problem, and obtain a family of exact solutions in the form of single solitons and soliton trains. We interpret the collective oscillations as Bloch precession of Anderson pseudospins, where each soliton causes a pseudospin full Rabi rotation. Numerical simulations demonstrate robustness of the solitons with respect to noise and damping.