Scientists have demonstrated an extraordinary form of quantum matter that combines two properties that seem incompatible. Known as a supersolid, this unusual state has the orderly structure of a crystal while also displaying the frictionless flow associated with a special kind of liquid. Even more remarkably, researchers have now observed this behavior at room temperature, eliminating the need for the extreme cooling traditionally used to investigate such phenomena.
The breakthrough was achieved by an international team 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). Rather than relying on atoms cooled to temperatures near absolute zero, the scientists created a supersolid using particles that combine properties of light and matter.
Published in Science Advances, the findings introduce a new way to investigate exotic quantum behavior under much more accessible conditions. They could also help advance future technologies ranging from optical computing to highly sensitive sensors.
How Can Matter Behave Like Both a Solid and a Liquid?
Under ordinary circumstances, solids and liquids behave very differently. Crystals have an organized internal structure, with their particles arranged in repeating patterns. Liquids, by comparison, can flow and change shape.
Quantum physics, however, allows matter to behave in ways that would be impossible under the familiar rules of everyday life.
One example is superfluidity, a remarkable phenomenon in which a fluid loses its viscosity, or internal resistance to flowing. A superfluid can move through extremely narrow passages without experiencing the usual friction. Imagine placing an oar into such a liquid. You would encounter almost no resistance until the oar reached a certain speed. Beyond that threshold, tiny swirling structures known as quantum vortices would suddenly form.
During the 1960s, physicists proposed an even stranger possibility. What if a superfluid could also develop the repeating internal structure normally associated with a crystal?
This hypothetical combination became known as a supersolid. In such a state, the material exhibits the spatial organization of a solid while retaining the remarkable flow properties of a superfluid.
For decades, supersolidity remained a theoretical concept. Experimental confirmation finally arrived in 2017, when researchers observed the phenomenon in ultracold atomic Bose-Einstein condensates. These condensates form when particles enter a collective quantum state and begin behaving as a coordinated system rather than as separate individuals.
The catch was that producing these conditions generally required sophisticated equipment capable of cooling matter to temperatures extremely close to absolute zero, the lowest possible temperature.
Creating a Quantum Supersolid Using Light Instead of Cold Atoms
The international TopoLight consortium approached the challenge from a different direction. Instead of using ultracold atoms, the researchers worked with unusual hybrid particles called exciton polaritons.
These quasiparticles arise when light interacts so strongly with matter that the two become coupled inside a tiny optical chamber called a microcavity. The resulting particles display characteristics of both light and matter.
Exciton polaritons are extremely short-lived, typically surviving for only a few picoseconds. A picosecond is one trillionth of a second. Despite their brief existence, these particles can organize into a Bose-Einstein condensate and collectively exhibit the behavior of a quantum superfluid.
To create the necessary conditions, the team constructed an optical microcavity containing a specially engineered liquid crystal and covered it with an organic semiconductor. The arrangement allowed light and matter to interact strongly enough to produce the desired quantum effects without the need for extreme cooling.
“Our liquid-crystal microcavities can operate even at temperatures approaching 60°C,” says Professor Wiktor Piecek from the Military University of Technology, whose group developed the liquid-crystal structures.
That temperature is approximately 140°F, far above the freezing conditions normally associated with experiments involving exotic quantum matter.
Strange Patterns of Light Reveal a Supersolid
How can researchers determine whether a collection of particles has entered such an unusual state?
In this experiment, the evidence appeared in the light emitted by the sample. When the system transitioned into the supersolid phase, researchers observed a series of regularly spaced bright fringes.
These patterns indicated that the particle condensate had spontaneously developed a repeating variation in its density. This type of spatial organization is a defining feature of crystalline structures and an important sign of supersolidity.
But the researchers noticed another intriguing effect.
Each time a laser pulse excited the sample, the bright fringes appeared in a different position. Rather than following a single fixed arrangement, the quantum system repeatedly selected among several equally possible configurations.
“This is a textbook example of spontaneous symmetry breaking,” explains Professor Guillaume Malpuech from Institut Pascal (CNRS). “Theory predicted that the supersolid could choose among several equivalent states, and that is exactly what we observed.”
Spontaneous symmetry breaking occurs when a system that could exist in several equivalent arrangements settles into one particular configuration. In this case, the effect became visible through the changing positions of the light patterns.
The condensate also displayed another unusual characteristic called a persistent spin helix. This refers to a repeating variation in the polarization of the emitted light. Polarization describes the orientation of light’s oscillating electric field.
Together, these observations revealed two different forms of order occurring at the same time. One appeared in the intensity of the emitted light, while the other appeared in its polarization.
A Difficult Experiment With Only Hours to Succeed
Achieving these results required overcoming an unexpected practical obstacle.
The organic semiconductor used in the device gradually reacted with the liquid crystal. As a result, the experimental samples had a limited useful lifetime, giving the scientists only a few hours to collect their measurements after assembly.
This restriction made careful preparation essential. The researchers needed to determine exactly which measurements to perform and in what order before beginning each experimental run.
“We had to plan the entire sequence of experiments in advance,” recalls Dr. Marcin Muszyński, the paper’s first author, now a postdoctoral researcher at The City College of New York. “Repeating a measurement meant fabricating an entirely new sample.”
The most important measurements took place at IBM Research Zurich. There, scientists deposited thin layers of the organic semiconductor onto specialized structures designed to manipulate light. These photonic structures had been manufactured at the Military University of Technology.
The semiconductor itself was not new to the researchers. IBM scientists had investigated its quantum properties for years, including its ability to support Bose-Einstein condensation.
“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,” says Thilo Stöferle from IBM Research. “This was the first time we combined it with a liquid-crystal microcavity.”
Bringing these materials together ultimately made it possible to observe the unusual supersolid behavior at room temperature.
Why Room Temperature Quantum Matter Matters
The significance of the discovery extends beyond demonstrating another unusual phenomenon predicted by quantum physics.
Many experiments involving exotic quantum states depend on costly cryogenic systems designed to maintain temperatures close to absolute zero. These demanding conditions make research more complicated and can create substantial obstacles when scientists attempt to turn laboratory discoveries into useful technologies.
The new results show that certain exotic quantum effects can instead be investigated in photonic devices that operate at ordinary temperatures.
This could create opportunities for future technologies that use light to process information. Potential applications include ultrafast photonic devices, specialized computing accelerators inspired by the way biological brains process information, and advanced optical sensors.
The computing approach, known as neuromorphic computing, seeks to imitate aspects of the brain’s information processing to perform certain tasks more efficiently. Light-based systems could eventually provide new ways to accelerate these operations.
The supersolid’s exceptional sensitivity to light polarization may also prove useful for developing sensors capable of detecting extremely subtle optical changes.
These applications remain possibilities for future research, but the ability to generate the underlying quantum behavior without extreme cooling represents an important step toward making such technologies more practical.
Electrically Controlled Quantum Matter Opens New Possibilities
One of the most promising features of the experiment is that the optical device can be adjusted using electricity.
The liquid crystal microcavities provide the first electrically tunable platform for studying supersolid exciton-polariton condensates. This means researchers can alter the optical properties of the system by applying an external voltage.
Earlier experimental approaches did not offer this same degree of electrical control.
The ability to adjust the system dynamically gives physicists greater flexibility when investigating how quantum states emerge, interact, and respond to changing conditions.
It could also become valuable when designing practical quantum photonic devices, where precise control over the behavior of light and matter is essential.
By combining room-temperature operation with electrical tunability, the researchers have established a versatile platform for exploring quantum phenomena that previously required far more demanding experimental conditions.
About the University of Warsaw Faculty of Physics
The University of Warsaw has a long history of research and education in physics and astronomy. Both disciplines became part of the university in 1816, when they were included in the Faculty of Philosophy. The university subsequently established its Astronomical Observatory in 1825.
Today, the Faculty of Physics includes the Institutes of Experimental Physics, Theoretical Physics, and Geophysics, along with the Department of Mathematical Methods in Physics.
Its research encompasses nearly every major area of modern physics, from the behavior of particles at quantum scales to the structure and evolution of the universe.
The faculty employs more than 250 academic teachers and serves approximately 1,350 students and more than 150 doctoral students.
According to Shanghai’s Global Ranking of Academic Subjects, the University of Warsaw ranks among the world’s top 150 institutions for physics education.