We observe evidence of first-order superfluid-to-Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include the hysteresis effect, significant heatings across the phase transitions, and changes in spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory and suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid-to-Mott-insulator phase transitions.
The Mott insulator and superfluid phase transition is one of the most prominent phenomena in ultracold atoms. In this work, we report the observation of a novel 2D quantum phase transition between Mott insulator and
π 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
px,y bands are itinerant for having larger bandwidth. Through a shaking technique coupling the
s orbital to
px,y orbital states, we experimentally observe the transition between the states of the
s and
px,y bands, leading to a quantum phase transition from 2D
s-orbital Mott phase to the
px,y-orbital superfluid which condensed at
(π,π) momentum.