Ultracold atoms in optical lattices offer a versatile platform for exploring quantum many-body physics as well as fundamental photon-atom interactions. In this talk, I will present experimental results from the BEC5 apparatus at MIT, where we use lithium-7 atoms to study two distinct classes of phenomena.

First, I will show how a Mott insulator in an optical lattice enables clean studies of light scattering. We begin by showing the simple case of scattering from individual atoms, where the concept of coherence and how it manifests in arrays is showcased. The problem can be extended to the more interesting case of light scattering from tightly confined atom pairs, where the light-induced dipole-dipole interaction between atoms modifies the coherence and motion of the atom pair during the scattering process. We also demonstrate an interesting interplay with Feshbach resonance.

Then, I will discuss how we study spin physics using the superexchange interactions in a Mott insulator. Specifically, we investigated the properties of an xy-ferromagnet in the anisotropic Heisenberg model. We show how the ground state can be prepared through adiabatic sweep. We also demonstrate spin squeezing, which is theoretically known to be related to a phase transition to an xy-ferromagnetic phase.