Observation of many-body physics and two-body Lamb shift using light scattering*

We report on an experiment using light scattering to explore many-body physics in an optically densed atomic sample in a three-dimensional optical lattice. We collect the light scattering of a near-resonant pulse at a non-Bragg angle. We perturbatively scatter ~0.3 photon per atom from a 3D optical lattice with ~50k atoms and collect ~100 photon on an EMCCD camera. At a non-Bragg angle, the light scattering is suppressed due to the lack of resonance in the lattice structure factor. We compare the collected fluorescence before and after a short release from the 3D lattice to extract a suppression factor. This lack of Bragg enhancement is ideal to study the coherence properties of a single atom light scattering, the atom number fluctuation over the lattice sites etc. As a initial test, we verify the mean field theory of superfluid-Mott insulator transition and Kibble-Zurek mechanism during non-adiabatic ramping process in a 3D lattice.

In a deep lattice with two atoms on one lattice site, whose Wannier function size is less than 30 nm, the atomic resonance is expected to have a shift on the order of transition linewidth. We use light scattering coherence, atomic explosion observed at far field absorption imaging or insitu spectroscopy to detect the near field two body collective Lamb shift (CLS).