Light-Based Supersolid Seen at Room Temperature, No Deep Freeze Needed

An international team of physicists says it has created a supersolid, a quantum state that is both crystal-like and frictionless, at room temperature. Until now, such states were observed only in atoms cooled to temperatures extremely close to absolute zero, according to a University of Warsaw release published by ScienceDaily on Nov. 9.

The researchers, from the University of Warsaw, the Military University of Technology in Poland, IBM Research Zurich and France's CNRS, built the supersolid from hybrid particles of light and matter instead of ultracold atoms. The findings were published in Science Advances. The team says the approach could ease the study of exotic quantum behavior and may eventually help optical computing and sensing technologies.

What a supersolid is

Solids and liquids normally behave very differently. A crystal has particles arranged in repeating patterns, while a liquid flows and changes shape.

Quantum physics allows stranger combinations. One is superfluidity, in which a fluid loses its viscosity, the internal resistance to flowing. According to the release, an oar moved through a superfluid would meet almost no resistance until it reached a certain speed. Past that point, tiny swirls called quantum vortices would suddenly form.

In the 1960s, physicists proposed that a superfluid might also develop the repeating structure of a crystal. This hypothetical state became known as a supersolid. It remained theoretical for decades. Experimental confirmation came in 2017, in ultracold atomic Bose-Einstein condensates, which form when particles enter a shared quantum state and act as a coordinated system. Reaching that state generally required sophisticated equipment to cool matter close to absolute zero.

How the team used light instead of cold

The team, working as the TopoLight consortium, used particles called exciton polaritons. These quasiparticles arise when light and matter interact so strongly inside a tiny optical chamber, a microcavity, that they become coupled. The result shows traits of both.

Exciton polaritons are extremely short-lived, typically lasting only a few picoseconds. A picosecond is one trillionth of a second. Even so, they can form a Bose-Einstein condensate and act collectively as a quantum superfluid.

The researchers built a microcavity containing a specially engineered liquid crystal and covered it with an organic semiconductor. This setup let light and matter interact strongly enough to produce the quantum effects without extreme cooling. Professor Wiktor Piecek of the Military University of Technology, whose group developed the liquid-crystal structures, said the microcavities can work at temperatures approaching 60°C. That is about 140°F.

The evidence: bright stripes that shift

The signal came from the light emitted by the sample. When the system entered the supersolid phase, the researchers saw regularly spaced bright fringes. According to the release, these showed that the condensate had spontaneously developed a repeating variation in density, a defining feature of crystalline structure and an important sign of supersolidity.

The team also saw that the fringes did not stay put. Each time a laser pulse excited the sample, they appeared in a different position. The system repeatedly chose among several equally possible arrangements. Professor Guillaume Malpuech of Institut Pascal (CNRS) described this as a textbook example of spontaneous symmetry breaking. He said theory had predicted that a supersolid could pick among several equivalent states.

Why it matters

For most readers, the news is not about a product. It concerns how hard it has been to study exotic quantum matter. Ultracold experiments need specialized cooling equipment, which limits who can run them and what can be built on them. A system that shows supersolid behavior at room temperature points to a more accessible way to explore these states.

The researchers say the work could help bring light-based technologies closer, including optical computing and highly sensitive sensors. Those are described as possible future applications, not devices that exist today. The result is a laboratory demonstration from a single research effort, and the release does not describe independent confirmation or a timeline for practical uses.

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Around Prague, based on reporting by ScienceDaily