Tunable Single-Ion Anisotropy in Spin-1 Models Realized with Ultracold Atoms

Mott insulator plateaus in optical lattices are a versatile platform to study spin physics. Using sites occupied by two bosons that possess an internal degree of freedom in the form of a hyperfine state, we realize a Hamiltonian with a uniaxial single-ion anisotropy term proportional to (S_z)² which plays an important role in stabilizing magnetism for low-dimensional magnetic materials. The ground states of the Hamiltonian include a spin Mott insulating phase, which can be adiabatically connected to the correlated XY ferromagnet. We explore non-equilibrium spin dynamics after preparing a rotated spin state, which is quenched into a Hamiltonian with nonzero superexchange. We observe a resonant effect in the spin alignment as a function of lattice depth when the exchange coupling and on-site anisotropy are similar. Our results are supported by many-body numerical simulations, and the essential physics is captured by the analytical solution of a two-site model.