Researchers from the University of Warsaw, Research Zurich, the Military University of Technology (Poland) and the French National Centre for Scientific Research ( ) have observed a new quantum state of matter known as a supersolid in an exciton-polariton Bose-Einstein condensate. This achievement departs significantly from the 2017 observation of supersolidity, which required temperatures near absolute zero, and used exciton-polariton Bose-Einstein condensates instead of ultracold atomic condensates.

“Our liquid-crystal microcavities can operate even at temperatures approaching 60°C,” says Professor Wiktor Piecek of the Military University of Technology, whose group developed the liquid-crystal structures, potentially opening new avenues for studying and applying this paradoxical state of matter.

Exciton-Polariton Condensate Enables Room-Temperature Supersolid Observation

This unexpected result stemmed from the use of an exciton-polariton Bose-Einstein condensate, a fundamentally different approach than the 2017 observation of supersolidity relying on ultracold atomic gases. Researchers used a unique system combining this condensate with a liquid-crystal microcavity, a configuration that allowed for room-temperature operation and observation of the phenomenon. “This was the first time we combined it with a liquid-crystal microcavity,” noted a researcher involved in the study.

The organic semiconductor gradually reacted with the liquid crystal, meaning that all measurements had to be completed within only a few hours after the sample was assembled. Each measurement necessitated the fabrication of an entirely new sample, a demanding process. “Repeating a measurement meant fabricating an entirely new sample,” they explained, highlighting the experimental challenges overcome to verify the findings. The observed supersolid exhibited a peculiar behavior, spontaneously selecting one of several equivalent configurations with each laser pulse used to excite the sample.

This selection process, revealed by shifts in the position of the bright fringes, demonstrated a key characteristic of the state. “Theory predicted that the supersolid could choose among several equivalent states, and that is exactly what we observed,” said Professor Guillaume Malpuech from Institut Pascal. A supersolid’s paradoxical nature arises from its simultaneous display of superfluidity, flow without any viscosity and a periodic, crystal-like structure.

This combination of properties, seemingly at odds with one another, challenges conventional understanding of matter. Professor Jacek Szczytko, University of Warsaw, and colleagues have demonstrated a new pathway to creating and studying supersolidity, opening possibilities for future investigations into its fundamental properties and potential applications.

Our liquid-crystal microcavities can operate even at temperatures approaching 60°C.
Wiktor Piecek, Professor from the Military University of Technology

Liquid-Crystal Microcavity Design Facilitates Strong Light-Matter Coupling

At 60°C, a temperature significantly above the near-absolute-zero conditions required by previous observations of supersolidity, the team observed a quantum supersolid state. Researchers used strong light-matter coupling within a specifically designed system to achieve this result. The optical microcavity central to the experiment contained a liquid crystal and an organic semiconductor, enabling the strong coupling necessary for the observation. This electrical tunability provides flexibility for investigating quantum phases of light and matter, potentially leading to practical quantum photonic devices.

The observed supersolid exhibited spontaneous symmetry breaking, a phenomenon where the system selects one of several equivalent possibilities; “This is a textbook example of spontaneous symmetry breaking,” noted a researcher. The ability to manipulate and study this behavior at room temperature could accelerate the development of ultrafast photonic devices, neuromorphic computing accelerators and highly sensitive optical sensors.

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.
Thilo Stöferle, IBM Research

Spontaneous Symmetry Breaking Confirms Supersolid Phase Transition

This selection process confirms a key theoretical prediction about supersolids. The system doesn’t simply settle into one ordered arrangement, but actively chooses from a range of possibilities. The appearance of regularly spaced bright fringes signaled the transition into the supersolid phase, indicating the condensate had spontaneously formed a periodic density modulation, a defining characteristic of crystallization. This observation, detailed in Science Advances, provides direct evidence of the interplay between superfluidity and crystalline order within the exciton-polariton condensate.

The Faculty of Physics at the University of Warsaw contributes significantly to the global research landscape, currently ranking among the top 200 universities worldwide according to Shanghai’s Global Ranking of Academic Subjects. With over 250 academic teachers and a combined student body of over 250, including doctoral candidates, the Faculty’s research extends beyond this discovery, as evidenced by its press service available online.