Supersolidity in a driven quantum gas

Driven systems are of fundamental scientific interest, as they can display properties that are radically different from similar systems at equilibrium. However, systems out of equilibrium are difficult to describe theoretically, as they are inherently time-dependent and deeply nonlinear. This makes the study of such systems an ideal task for quantum field simulators, in which complex dynamics emerge naturally and can be probed experimentally. Here, we demonstrate the emergence of supersolidity in a driven, two-dimensional superfluid that only has contact interactions. The self-stabilized system emerges as a result of large occupations of phononic modes due to driving [1] and can be described theoretically using an out-of-equilibrium fixed point of amplitude equations [2]. To demonstrate the hallmarks of supersolidity, we induce collective modes of the lattice, and show that the system supports lattice phonon propagation. We also show that the state maintains phase rigidity, a key property of superfluidity. This work introduces a novel type of supersolid that is readily experimentally accessible, and establishes a conceptual framework for describing elementary excitations of driven systems.

[1] N. Liebster, et al., arXiv:cond-mat/2309.03792 (2023)

[2] K. Fujii, et al., arXiv:cond-mat/2309.03829 (2023)