Observation of Two-Dimensional Mott Insulator and π-Superfluid Quantum Phase Transition in Shaking Optical Lattice

The Mott insulator and superfluid phase transition is one of the most prominent phenomena in ultracold atoms. We report the observation of a novel 2D quantum phase transition between the Mott insulator and πsuperfluid in a shaking optical lattice. In the deep optical lattice regime, the lowest S band can be tuned to Mott phase, while the higher Px,y bands are itinerant for having larger bandwidth. Through a shaking technique coupling the s-orbital to px,y-orbital states, we experimentally observ...