Researchers in Europe have demonstrated an extraordinary form of quantum matter where light behaves simultaneously like an orderly crystal and a frictionless liquid at room temperature.
Published in Science Advances, the findings bridge theoretical quantum physics and accessible photonic engineering.
Solids and liquids normally maintain distinct structural rules. Crystals feature repeating internal patterns, whereas liquids flow and change shape without fixed spatial organization. During the 1960s, physicists proposed that a superfluid could theoretically develop a repeating internal structure, creating a hybrid known as a supersolid.
Experimental confirmation arrived in 2017 when researchers observed supersolidity in ultracold atomic Bose-Einstein condensates. Producing those states required extreme equipment capable of cooling matter down close to absolute zero. The newly reported international collaboration eliminates that cryogenic barrier entirely by abandoning cold atoms for hybrid quasiparticles.
The international TopoLight consortium formed quasiparticles called exciton polaritons inside an optical microcavity. These entities emerge when light couples tightly with matter, displaying characteristics of both domains for just a few picoseconds. Despite their brief lifespan, these hybrid particles form a Bose-Einstein condensate that exhibits superfluid behavior.
To bypass cryogenic limitations, the team constructed an optical microcavity using a specially engineered liquid crystal covered by an organic semiconductor. Professor Wiktor Piecek from the Military University of Technology stated, Our liquid-crystal microcavities can operate even at temperatures approaching 60°C,
noting this equals roughly 140°F.
Evidence of the supersolid state appeared directly in the light emitted by the test sample. When the system entered the supersolid phase, researchers detected regularly spaced bright fringes indicating a spontaneous density variation.
The condensate simultaneously produced a persistent spin helix, revealing two forms of order occurring in both intensity and polarization.
Executing the experiment required precise advance planning due to chemical reactions between the organic semiconductor and the liquid crystal. Thin layers of the organic semiconductor MeLPPP were deposited at IBM Research Zurich onto photonic structures manufactured at the Military University of Technology.
Thilo Stöferle from IBM Research stated, We have studied the organic semiconductor MeLPPP (methyl-substituted ladder-type poly(paraphenylene) for many years and previously observed Bose-Einstein condensation in this material,
highlighting that this marked the first time the compound was combined with a liquid-crystal microcavity.
