Physicists Make a Supersolid From Light Near 60°C, No Deep Freeze
Researchers report a supersolid made of light-matter particles at room temperature, with no extreme cooling. Here is how the experiment worked and its limits.
A team from Poland, Switzerland and France reports a supersolid at room temperature, a quantum state that has the repeating structure of a crystal and the frictionless flow of a superfluid. According to the University of Warsaw Faculty of Physics, the result was published in Science Advances. Earlier supersolids needed atoms cooled close to absolute zero.
The group built the supersolid from hybrid particles of light and matter instead of cold atoms. The researchers say this opens a way to study exotic quantum behavior with far simpler equipment, though applications such as optical computing and sensing remain possibilities for future work.
What a supersolid is
A superfluid is a fluid with no viscosity, so it can move through very narrow passages without friction. In the 1960s, physicists proposed that a superfluid might also form a repeating, crystal-like pattern. That hypothetical state was called a supersolid. It was first confirmed experimentally in 2017, in ultracold atomic Bose-Einstein condensates, where particles settle into one collective quantum state. Those experiments required cooling matter to temperatures extremely close to absolute zero.
How the team built it
The international TopoLight consortium used exciton polaritons, quasiparticles that appear when light couples strongly with matter inside a tiny optical chamber called a microcavity. They last only a few picoseconds, a picosecond being one trillionth of a second. Even so, they can form a Bose-Einstein condensate and act as a quantum superfluid.
The researchers made a microcavity containing an engineered liquid crystal and covered it with an organic semiconductor. Professor Wiktor Piecek of the Military University of Technology, whose group developed the liquid-crystal structures, said the microcavities can operate at temperatures approaching 60°C. The semiconductor, MeLPPP, had been studied for years at IBM Research Zurich, where it previously showed Bose-Einstein condensation. This was the first time it was combined with a liquid-crystal microcavity, according to IBM’s Thilo Stöferle.
How they know it is a supersolid
The evidence is in the light the sample emits. When the system entered the supersolid phase, regularly spaced bright fringes appeared, showing that the condensate had developed a repeating variation in density, a mark of crystalline order.
The fringes also appeared in a different position after each laser pulse, as the system picked among several equally possible arrangements. Professor Guillaume Malpuech of Institut Pascal (CNRS) called this “a textbook example of spontaneous symmetry breaking,” and said theory had predicted the supersolid could choose among equivalent states.
The condensate also showed a persistent spin helix, a repeating variation in the polarization of the emitted light. That gave two kinds of order at once: one in intensity, one in polarization.
A short window for measurements
The organic semiconductor slowly reacted with the liquid crystal, so each sample was usable for only a few hours. Dr. Marcin Muszyński, the paper’s first author, now at The City College of New York, said the team had to plan the whole sequence in advance, because repeating a measurement meant making a new sample. The key measurements were done at IBM Research Zurich, on photonic structures made at the Military University of Technology.
Why it matters
Many quantum experiments depend on costly cryogenic systems, which complicate research and make it harder to turn lab results into devices. The new work shows certain exotic quantum effects can be studied in photonic devices at ordinary temperatures.
The authors list possible uses: ultrafast photonic devices, computing accelerators modeled on how brains process information (neuromorphic computing), and sensors able to detect very small optical changes, since the supersolid is highly sensitive to light polarization. These are described as directions for future research, not demonstrated products.
The device is also the first electrically tunable platform for studying supersolid exciton-polariton condensates, according to the team. Applying a voltage changes its optical properties, a degree of control earlier experimental approaches did not offer.
Source: ScienceDaily
