This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers from the Faculty of Physics at the University of Warsaw, the Military University of Technology (Poland), IBM Research Zurich and the French National Centre for Scientific Research (CNRS) have observed a new quantum state of matter known as a supersolid in an exciton-polariton Bose-Einstein condensate. Remarkably, the phenomenon occurs not at temperatures close to absolute zero, but at room temperature.
The results have been published in Science Advances. At first glance, this seems impossible. A crystal is rigid and ordered, while a liquid flows.
Yet quantum mechanics allows a state that combines both properties. The story begins with superfluidity—an extraordinary state of matter in which viscosity completely disappears. A superfluid can flow through the narrowest channels without resistance.
If you dipped an oar into such a liquid, you would feel almost no drag until a critical velocity was exceeded, at which point quantum vortices would suddenly appear. As early as the 1960s, physicists predicted that a superfluid could simultaneously develop a periodic crystal-like structure. The resulting phase, called a supersolid, retains the frictionless flow of a superfluid while exhibiting the spatial order of a crystal.
For more than half a century, this remained a theoretical prediction. It was not until 2017 that supersolidity was experimentally observed in ultracold atomic Bose-Einstein condensates. The TopoLight consortium chose a completely different route.
Rather than using ultracold atoms, the researchers studied exciton polaritons—hybrid quasiparticles formed by the strong coupling between light and matter inside an optical microcavity. Although they exist for only a few picoseconds, this is sufficient for them to form a Bose–Einstein condensate and behave as a quantum superfluid. The optical microcavity was filled with a specially designed liquid crystal and coated with an organic semiconductor.
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