Floquet Phase Transitions in Strongly-Driven Optical Lattices*

Ultracold neutral atoms in driven optical lattices provide a rich test bed for exploring non-equilibrium physics. We report on experimental characterization of a Floquet phase diagram using ultracold bosonic lithium in a strongly-driven optical lattice. As the drive frequency and amplitude are tuned,we observe a sharp transition line between stable and unstable behavior. For deep lattices and zero interactions, this transition corresponds to the classically-expected threshold for chaos. We explore the effect of Feshbach-tunable interactions and lattice-tunable tunneling on the properties of this Floquet phase diagram.