Observation of Two-Dimensional Mott Insulator and & pi;-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 & pi; superfluid in a shaking optical lattice. In the deep optical lattice regime, the lowest S band can be tuned to Mott phase, while the higher p(x,y) bands are itinerant for having larger bandwidth. Through a shaking technique coupling the s-orbital to p(x,y) -orbital states, we experimentally observe the transition between the states of the S and p(x,y) bands, leading to a quantum phase transition from two-dimensional s-orbital Mott phase to the p(x,y) -orbital superfluid which condensed at (& pi;, & pi;) momentum. Using the band-mapping method, we also observe the changes of atomic population in different energy bands during the transition, and the experimental results are well consistent with theoretical expectations.

Automated summary

We report the observation of a 2D quantum phase transition from Mott insulator to π superfluid in a shaking optical lattice. Through a shaking technique, we experimentally observe the transition between the S and p(x,y) bands, resulting in a quantum phase transition from 2D s-orbital Mott phase to p(x,y) orbital superfluid condensed at (π,π) momentum. Using the band-mapping method, we observe the changes of atomic population in different energy bands during the transition, which are consistent with theoretical expectations.