An international group of researchers has produced an exotic quantum state of matter — a supersolid — inside a small light-confining device known as a microcavity, and did so without the deep cooling that such experiments normally demand. The findings were published in Science Advances and reported by ScienceAlert, with Phys.org describing the system as light-matter hybrids forming a supersolid at room temperature.
According to ScienceAlert, the structure can function at temperatures approaching 60 °C (140 °F), a figure attributed to physicist Wiktor Piecek of the Military University of Technology in Poland. That is far above the near-absolute-zero conditions typical of quantum experiments, and it points toward cheaper, more practical routes to quantum computing hardware and sensors.
Why it matters
Quantum effects are usually fragile. They tend to survive only when a sample is chilled to within a fraction of a degree of absolute zero, which requires cryogenic refrigerators and adds cost, bulk and complexity to any experiment or device.
The setup described here sidesteps that requirement. ScienceAlert reports that the microcavity platform is relatively inexpensive, can be tuned by applying voltages, and needs no cryogenic fridge at all. If the approach holds up, it would give researchers a more accessible testbed for studying quantum fluids of light — and, eventually, a foundation for technologies that depend on those effects.
What a supersolid actually is
The full technical label for the state is a supersolid within an exciton-polariton Bose-Einstein condensate. Each part of that phrase describes something distinct.
A superfluid is a liquid that flows with no resistance. A supersolid is a superfluid that also arranges itself into a regular, repeating crystal structure instead of flowing loosely. That is the supersolid component.
An exciton-polariton is a quasiparticle — several particles behaving as a single unit — that blends light and matter. A Bose-Einstein condensate, meanwhile, is a condition in which many particles or quasiparticles merge into one collective quantum entity.
To create the state, the team paired a liquid crystal, which responds to voltage, with an organic semiconductor that interacts strongly with light. Laser pulses delivered the energy needed to drive the reaction, according to ScienceAlert.
Short-lived signals, repeatable results
The observations were not long-lived. The materials degraded over time as the semiconductor reacted with the liquid crystal, ScienceAlert reports. That constraint shaped how the work had to be done.
"We had to plan the entire sequence of experiments in advance," physicist Marcin Muszyński of the City College of New York told ScienceAlert. "Repeating a measurement meant fabricating an entirely new sample."
Each successive laser pulse provided fresh confirmation of what the researchers were seeing. The condensate re-formed every time, and its stripes — the crystal-like portion of the supersolid — settled into slightly different positions with each refresh.
ScienceAlert notes that this variation is meaningful: it indicates the behavior arises from the quantum state itself rather than from the surrounding microcavity. Physicist Guillaume Malpuech of the French National Centre for Scientific Research (CNRS) called it a textbook case of spontaneous symmetry breaking, telling ScienceAlert that theory had predicted the supersolid could select among several equivalent states, and that the experiments showed exactly that.
Individual particles persisted only for fractions of a second, but that window was sufficient for the measurements. Multiple samples produced consistent results, and computer simulations backed them up.
Open questions and next steps
The researchers also observed quantum vortices — irregularities in the stripe patterns that signal superfluid behavior — and ScienceAlert reports that these deserve closer examination. Extending how long the core reactions last is another obvious target for follow-up work.
The broader significance, per the team's published paper, lies in what the platform makes easier to study: spin-orbit coupling, the link between light polarization and motion that produced the supersolid arrangement, can now be examined without the expense and difficulty of extreme refrigeration. ScienceAlert notes that nearly any light-based quantum effect, including those relevant to computer chips and advanced sensors, could benefit over time.
"Our work opens new perspectives for quantum fluids of light physics in the presence of spin-orbit coupling and beyond," the researchers wrote in Science Advances.
Watch for follow-up studies aimed at lengthening the state's lifetime and probing the vortices in more detail — and for attempts to reproduce the result on other liquid-crystal and semiconductor combinations.
