Observation of atomic Fock state interference 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.

More interestingly, we find an oscillation of light scattering amplitude due to the interference effect between identical atoms in Fock states. To observe this quantum statistical effect, we turn off the one vertical lattice along the observation angle for various one-dimensional time-of-flight duration to allow wave packets to overlap. Atomic wave packet pairs in neighboring sites interfere with each other and show constructive or destructive interference (fluorescence strength) as we vary the TOF duration. Since the light scattering experiment is effectively a correlation measurement, intensity signal from all these pairs are additive, despite the fact that Fock states have random phases. Our experiment can be interpreted as a near-field HBT experiment. Due to their different quantum statistics, we could observe opposite oscillation phase for fermionic and bosonic isotopes of dysprosium.