Originally predicted at the end of the 1960s, researchers still can’t say with certainty that they have actually observed the supersolid phase of matter in the laboratory. Physicists in Austria now report that they have found further evidence for this phase in a Bose-Einstein condensate made of erbium atoms. The finding will help advance our understanding of how spontaneous symmetry breaking occurs in quantum systems, they say. It also confirms that ultracold atoms are a powerful test bed in which to study highly non-trivial quantum phenomena.

A supersolid is a paradoxical form of matter – it flows without friction (like a superfluid) but its particles are arranged in a crystalline lattice (like a solid). Indeed, it is described as being a state in which two continuous symmetries are broken at the same time. These are: the translational invariance, which is associated with crystalline order; and the gauge symmetry, which is associated with the material’s frictionless flow.

“The remarkable thing about a supersolid phase is that it has a dual nature in which two antithetic orders co-exist,” explains study team leader Francesca Ferlaino of the University of Innsbruck. “A supersolid is in fact both a crystal and a superfluid.”

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