In 1938, one year after the discovery of superfluidity in helium-4 (4He ), German physicist Fritz London proposed that superfluidity is linked to the congregation of atoms into the same quantum state: a Bose-Einstein condensate (BEC). Scientists now know that the two phenomena are related but not in an obvious way. For example, at low temperature, when liquid 4He becomes superfluid, only 14% of its atoms are in the same quantum state. In fact, some two-dimensional superfluids entirely lack a BEC component. Now Junheng Tao of the University of Maryland and collaborators show that the two phenomena are linked to a third: supersolidity [1]. The finding confirms the results of similar experiments performed earlier this year [2].

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