Supersolidity in ultra-cold dipolar gases

TL;DR

This paper reviews recent experimental and theoretical progress in realizing and understanding supersolidity in ultra-cold dipolar gases, highlighting key phenomena, results, and future research directions.

Contribution

It provides a comprehensive overview of the latest achievements and open questions in the study of supersolidity in dipolar quantum gases.

Findings

Observation of density modulations indicating supersolidity

Identification of Goldstone modes in dipolar gases

Discussion of potential future experiments like quantized vortices

Abstract

Can a gas behave like a crystal? Supersolidity is an intriguing and challenging state of matter which combines key features of superfluids and crystals. Predicted a long time ago, its experimental realization has been recently achieved in Bose-Einstein condensed (BEC) atomic gases inside optical resonators, spin-orbit coupled BEC's and atomic gases interacting with long range dipolar forces. The activity on dipolar gases has been particularly vibrant in the last few years. This perspective article summarizes the main experimental and theoretical achievements concerning supersolidity in the field of dipolar gases, like the observation of the density modulations caused by the spontaneous breaking of translational invariance, the effects of coherence and the occurrence of novel Goldstone modes. A series of important issues for the future experimental and theoretical research are outlined including, among others, the possible realization of quantized vortices inside these novel crystal structure, the role of dimensionality, the characterisation of the crystal properties and the nature of the phase transitions. At the end a brief overview on some other (mainly cold atomic) platforms, where supersolidity has been observed or where supersolidty is expected to emerge is provided.