Probing superexchange interactions in a 3D optical lattice clock*

Improving the stability of optical lattice clocks requires understanding mechanisms by which trapped atoms dephase from one another. In our setup, we achieve a nearly unity filled 3D optical lattice by loading a nuclear spin-polarized Fermi-degenerate gas. Applying the clock drive for spectroscopy removes the degeneracy of atoms along the clock propagation direction due to a spiral phase, allowing them to tunnel and interact and thus dephase. In this work, we launch the clock laser vertically, where a difference in gravitational potential between lattice sites strongly suppresses tunneling. To identify the optimal lattice geometry for clock operation, we map out the transition quality factor as a function of transverse and vertical lattice depths and identify two regions of interest in the parameter space. The first is the limit of weak transverse confinement, where we study the interplay of s- and p-wave interactions as we vary the vertical lattice depth. The second is deep confinement in both the transverse and vertical directions, where tunneling is suppressed but atoms can still interact and decohere via superexchange. We quantitively study this effect by observing both oscillations and reduction of our Ramsey fringe contrast as we vary the superexchange strength. Being able to observe and tune superexchange rates up to the timescale of a few seconds establishes the 3D lattice clock as a powerful tool for exploring quantum magnetism and entanglement and opens a potential new avenue for realizing spin-squeezing enhanced clock operation.