Dimension-Dependent, Tunable Spin Dynamics with Itinerant Ultracold Polar Molecules*

Ultracold molecules enable exploration of many-body physics due to their long-range, anisotropic dipolar interactions. With a microwave-addressable spin encoded in the two lowest rotational states of the molecules, motion controlled with optical lattices, and dipolar interactions tuned with d.c. electric fields, we realized a coupled spin-motion system of interacting molecules. In the motionless case, when molecules are pinned by a 3D optical lattice, their Ramsey contrast dynamics are well described by the XXZ Heisenberg spin model. When the molecules are free to move in either 1D tubes or 2D layers, molecular collisions modify the contrast decay rate differently for small and large electric fields. We attribute this effect to the difference between two collision channels of aligned and anti-aligned molecular pairs. Tuning between the fully pinned and the free moving extremes by allowing tunneling between lattice sites reveals further exciting behavior with a decoherence resonance appearing in 2D. This research marks the first time that t-J models have been explored with polar molecules, paving the way for future studies of kinetic spin models with the tunability of molecular platforms.