Matter that behaves like both a solid and a superfluid at the same time might sound impossible. But more than 50 years ago, physicists predicted that quantum mechanics could allow such a state. In this unique state, collections of particles exhibit properties that seem contradictory. Francesca Ferlaino from the Department of Experimental Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences explains, “It is a bit like Schrödinger’s cat, which is both alive and dead, a supersolid is both rigid and liquid.”
While scientists have managed to directly observe the crystalline structure that gives supersolids their “solid” qualities, their superfluid properties have been more elusive. Researchers have studied various aspects of superfluid behavior, like phase coherence and gapless Goldstone modes, but they had not found direct evidence of one key feature of superfluidity: quantized vortices.
In a major breakthrough, quantized vortices have now been observed in a rotating two-dimensional supersolid. This finding provides long-awaited proof of superfluid flow within a supersolid and marks a significant advance in the study of modulated quantum matter.
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