Atom-molecule theory of broad Feshbach resonances

Abstract

We derive the atom-molecule theory for an atomic gas near a broad Feshbach resonance, where the energy dependence of the atom-molecule coupling becomes crucial for understanding experimental results. We show how our many-body theory incorporates the two-atom physics exactly. In particular, we calculate the magnetic moment of a two-component gas of $^{6}\mathrm{Li}$ atoms for a wide range of magnetic fields near the broad Feshbach resonance at about $834\phantom{\rule{0.3em}{0ex}}\mathrm{G}$. We find excellent agreement with the experiment of Jochim et al. [Phys. Rev. Lett. 91, 240402 (2003)].