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.