Designing a quantum phase transition in a resonantly driven optical lattice

Phase transitions and critical phenomena have been at the heart of cold atom experiments from the beginning. While almost all phase transitions in cold atoms systems are continuous, there is a renewed interest in discontinuous (first-order) phase transitions and the associated metastable states, whose relativistic analogues are believed to play an important role in early-universe cosmology (false vacuum decay).

We experimentally demonstrate a novel level of control over a quantum phase transition by combining an optical lattice with an uncommon type of Floquet engineering based on a resonant drive. Contrary to most applications of periodic driving, where the drive frequency is selected to avoid all resonances, we resonantly couple the lowest two bands of a lattice. With this drive, we can not only induce the bosonic superfluid to Mott insulator transition but are furthermore able to control its character and turn the Mott transition from a continuous into a discontinuous transition.