Spin dynamics of ultracold atoms in optical lattices

In a Mott insulator, the motion of atoms is frozen out, and the study and control of the spin degree of freedom emerges as a new frontier. Ultracold atoms in optical lattices are an ideal platform to realize Heisenberg spin models and probe their dynamics. Until very recently, all experimental studies addressed the special case of an isotropic Heisenberg model. Using lithium-7 atoms and Feshbach resonances to tune the interactions, we have created spin ½ Heisenberg models with adjustable anisotropy, including the paradigmatic XX-model which can be exactly solved by mapping it to non-interacting fermions. Spin transport changes from ballistic to diffusive depending on the anisotropy. For transvers spin patterns, we have found several new dephasing mechanisms related to a superexchange induced effective magnetic field.

Using rubidium atoms and two atoms per site, we have realized spin 1 models. The onsite interactions give rise to a so-called-single-ion anisotropy term proportional to (S_z)^2, which plays an important role in stabilizing magnetism for low-dimensional magnetic materials. In the spin dynamics, we observe a resonant effect when this term and superexchange are comparable.

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