Fermionic Atoms in a Three Dimensional Optical Lattice: Observing Fermi Surfaces, Dynamics, and Interactions

TLDR

Gradual filling of the lattice transforms the system from a normal state into a band insulator due to the confining potential. The experiment probes quantum degenerate Fermi gases in a 3D optical lattice, imaging the Fermi surface adiabatically, measuring the transition dynamics from band insulator to normal state, and using a Feshbach resonance to induce interband coupling. The transition dynamics occur on a timescale an order of magnitude longer than the tunneling time, and the interband coupling shifts relative to the free‑space Feshbach resonance as expected for strongly confined atoms.

Abstract

We have studied interacting and noninteracting quantum degenerate Fermi gases in a three-dimensional optical lattice. We directly image the Fermi surface of the atoms in the lattice by turning off the optical lattice adiabatically. Because of the confining potential, gradual filling of the lattice transforms the system from a normal state into a band insulator. The dynamics of the transition from a band insulator to a normal state is studied, and the time scale is measured to be an order of magnitude larger than the tunneling time in the lattice. Using a Feshbach resonance, we increase the interaction between atoms in two different spin states and dynamically induce a coupling between the lowest energy bands. We observe a shift of this coupling with respect to the Feshbach resonance in free space which is anticipated for strongly confined atoms.