A "supersolid" state of matter — where atoms simultaneously flow like a liquid and maintain rigid crystalline order — has been created and directly observed in ultracold atomic gases for the first time.
Physics textbooks describe four states of matter: solid, liquid, gas, and plasma. A supersolid is something stranger — a material that simultaneously exhibits the rigid spatial order of a crystal and the frictionless flow of a superfluid. Theorists predicted this exotic state decades ago, and limited evidence had been found in helium experiments. But a new study from the University of Innsbruck and ETH Zurich has created and directly imaged a supersolid in a gas of dysprosium atoms cooled to just 50 nanokelvin — 50 billionths of a degree above absolute zero.
The supersolid defies everyday intuition because it requires two properties that normally exclude each other. A solid is defined by its atoms sitting in fixed positions relative to each other — they oscillate but don't flow. A superfluid flows without any viscosity, with atoms moving freely. In a supersolid, quantum mechanics allows both: the atoms maintain a repeating pattern in space (like a crystal lattice) while the quantum wavefunction that describes them extends coherently across the whole sample (like a superfluid). The result is a material that can flow through a hole without friction while also supporting the propagation of sound waves like a solid.
"A supersolid is not just a curiosity. Understanding it may tell us something fundamental about quantum matter that we simply could not access any other way."
— Senior physicist, ETH Zurich, 2026