Precise on-site dipole-dipole interaction spectroscopy of a dipolar atom Mott insulator

We investigate the magnetic interaction shift of two dysprosium atoms occupying one ~30 nm site in an atomic Mott insulator. This is achieved by driving a Δmj = 1 radiofrequency transition in the ground state manifold of Dy. The strong magnetic dipole interaction of Dy pairs may be reduced by angular averaging over the relative atom position, or hidden in the technical noise such as magnetic field drift. We maximize the net dipole effect by using tight, elongated lattice sites, and reducing the technical noise. Our measurement shows stronger attraction and weaker repulsion relative to mean-field calculation. We attribute the discrepancy to higher order spin-orbit coupling effect, which leads to a highly deformed pair relative wavefunction.