Nonlinear adiabatic passage from fermion atoms to boson molecules

Abstract

We study the dynamics of an adiabatic sweep through a Feshbach resonance in a quantum gas of fermionic atoms. Analysis of the dynamical equations, supported by mean-field and many-body numerical results, shows that the dependence of the remaining atomic fraction $Γ$ on the sweep rate $α$ varies from exponential Landau-Zener behavior for a single pair of particles to a power-law dependence for large particle number $N$. The power-law is linear, $Γ\propto α$, when the initial molecular fraction is smaller than the 1/N quantum fluctuations, and $Γ\propto α^{1/3}$ when it is larger. Experimental data agree better with a linear dependence than with an exponential Landau-Zener fit, indicating that many-body effects are significant in the atom-molecule conversion process.

5 pages, 4 figures