Observation of the supersolid stripe phase in spin-orbit coupled Bose-Einstein condensates

TL;DR

This paper reports the first direct observation of the supersolid stripe phase in a spin-orbit coupled Bose-Einstein condensate, demonstrating long-range order combined with superfluidity.

Contribution

It provides experimental evidence of the supersolid stripe phase in spin-orbit coupled BECs, confirming theoretical predictions and advancing understanding of supersolidity.

Findings

Direct observation of density modulation in the stripe phase

Confirmation of supersolid properties in spin-orbit coupled BECs

Establishment of a system with unique symmetry breaking

Abstract

Supersolidity is an intriguing concept. It combines the property of superfluid flow with the long-range spatial periodicity of solids, two properties which are often mutually exclusive. The original discussion of quantum crystals and supersolidity focuses on solid Helium-4 where it was predicted that vacancies could form dilute weakly interacting Bose-Einstein condensates. In this system, direct observation of supersolidity has been elusive. The concept of supersolidity was then generalized to include other superfluid systems which break the translational symmetry of space. One of such systems is a Bose-Einstein condensate with spin-orbit coupling which has a supersolid stripe phase. Despite several recent studies of this system, the stripe phase has not been observed. Here we report the direct observation of the predicted density modulation of the stripe phase using Bragg reflection. Our work establishes a system with unique symmetry breaking properties. Of future interest is further spatial symmetry breaking through the introduction of vortices, solitons, impurities or disorder.