Fermions in Optical Lattices across Feshbach Resonance

We point out that the recent experiments at ETH \cite{Esslinger} on fermions in optical lattices, where a band insulator evolves continuously into states occupying many bands as the system is swept adiabatically across Feshbach resonance, have implications on a wide range of fundamental issues in condensed matter. We derive the effective Hamiltonian of these systems, obtain expressions for their energies and band populations, and point out the increasing quantum entanglement of the ground state during the adiabatic sweep. Our results also explains why only specific regions in $k$-space can be populated after the sweep as found in ref. \cite{Esslinger}.