\"Projection onto Feshback Molecules as a probe of pairing, condensation and phase fluctuation induced psuedogap\"
We consider the nonequilibrium quantum problem of rapid sweeps across a Feshbach resonance, from the atomic (BCS) to the molecular (BEC) side, in an ultra cold Fermi system. We describe a simple model for this dynamics which allows us to relate equilibrium properties of the initial state to easily measurable final state properties, such as the fraction of condensed molecules, the momentum distribution of normal molecules and the conversion efficiency as a function of ramping rate. We find that this \'projection\' onto molecules is a very sensitive probe of pairs (both condensed and non-condensed paris) in the initial state, and arises ultimately from the short distance singularity of the Cooper pair wave function. We take into account the effects of phase fluctuations, which sharply reduce the observed condensate fraction even at zero temperature and can lead to a surprising nonmomotonic dependence of molecule condensate fraction on the intial state location. In addition to probing the fermion pair condensate [1,2], this approach can detect noncondensed pairs, and could possibly be a sensitive tool to study the phase fluctuation induced \"psuedogap phase\' expected in these systems.
1. C.A. Regal, M. Greiner, and D.S. Jin. Phys. Rev. Lett. 92, 040403 (2004).
2. M. Zwierlein, et al. Phys. Rev. Lett. 92, 120403 (2004)