Supersolids are a novel quantum phase of the matter recently discovered in a quantum gas of magnetic atoms, which combes the properties of superfluids and standard crystals. Although they were obtained experimentally by transforming a homogeneous superfluid, very little is known about the nature of the phase transition. Here, we find experimentally and theoretically that the superfluid-to-supersolid quantum phase transition resembles ordinary crystallization transitions but with important novelties due to the peculiar ways in which supersolids are different from both superfluids and solids. We see evidence of two types of transitions, continuous and discontinuous, which can be linked to the second-and first-order phase transitions expected for 1D and 2D systems, respectively. Interestingly, the dimensionality of a supersolid depends not only on the underlying lattice structure but also on the structure of the density background, which is a unique feature of supersolids that provides phase coherence among lattice sites. The continuous transitions we find provide access to excitation-free supersolids, which can be employed to study fundamental phenomena such as superfluidity and entanglement in this new state of matter.

The study was conducted by a collaborative team of researchers from INO-CNR, LENS and Università di Firenze.

Biagioni, N. Antolini, A. Alaña, M. Modugno, A. Fioretti, C. Gabbanini, L. Tanzi, and G. Modugno, Dimensional Crossover in the Superfluid-Supersolid Quantum Phase Transition, Phys. Rev. X 12, 021019 (2022), https://journals.aps.org/prx/abstract/10.1103/PhysRevX.12.021019