Dynamical pairing states in cold gases

Abstract

In this thesis, we study dynamical pairing of fermions caused by the time-dependent interaction. Fermionic pairing develops on time scales short compared to the quasiparticle relaxation time where existing approaches to the problem including the Boltzmann kinetic equation and time-dependent Ginzburg-Landau theory are not applicable. 'The nonequilibrium dynamics can be explored in cold Fermi gas at a Feshbach resonance, a system with magnetically tunable interaction. Motivated by recent experiments, in Chapters 2 and 3 we study the pairing of fermions when a sudden switch of interaction induces the Bardeen-Cooper-Schrieffer (BCS) instability of the system. In this case, the pairing amplitude is found to be an oscillatory function of time with predictable characteristics. Another dynamical regime corresponding to a linear magnetic field sweep from atomic to molecular side at a Feshbach resonance is explored in Chapter 4. We find that pairing correlations of fermions in the initial state are encoded in the momentum distribution of molecules after the sweep. Finally, in Chapter 5, we consider pair excitations caused by the harmonic modulation of the interaction, and compare our results to experimental observations.