A team including researchers from the University of Warsaw, IBM Research Zurich, and the French National Centre for Scientific Research (CNRS) has observed a supersolid state of matter within an exciton-polariton Bose-Einstein condensate, defying expectations by occurring at room temperature. Unlike previous observations requiring ultracold conditions, this phenomenon uses hybrid light-matter quasiparticles that exist for only a few picoseconds before forming the condensate and exhibiting superfluid behavior.
“Our liquid-crystal microcavities can operate even at temperatures approaching 60°C,” says Prof. Wiktor Piecek of the Military University of Technology, whose group developed the liquid-crystal structures used in the experiment. The resulting supersolid simultaneously displays the frictionless flow of a superfluid and the ordered structure of a crystal, confirmed by regularly spaced bright fringes and spontaneous symmetry breaking.
Exciton-Polariton Condensate Demonstrates Room-Temperature Supersolid Phase
The emergence of regularly spaced bright fringes in emitted light confirmed the formation of a periodic density modulation within the exciton-polariton condensate, a key indicator of crystallization and the supersolid phase. This observation marks the first time researchers have identified this quantum state within a condensate of hybrid light-matter quasiparticles, exciton-polaritons, rather than the ultracold atomic Bose-Einstein condensates used in a 2017 demonstration. The team’s approach used liquid-crystal microcavities, enabling operation at temperatures reaching 60°C, a significant departure from the ultracold conditions previously required, IBM Research says.
A researcher involved in the work explained, “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.” The ability to dynamically control the optical properties of these liquid-crystal microcavities with an external voltage provides a level of flexibility unseen in prior experiments. This constraint demanded meticulous planning, as the entire experimental sequence had to be predetermined before execution.
Repeating a measurement presented a fabrication challenge; each new data point necessitated the creation of an entirely new sample. “We had to plan the entire sequence of experiments in advance,” the team noted, highlighting the meticulous preparation required to capture the transient supersolid state. Despite the brief lifespan of the exciton-polaritons, lasting only a few picoseconds, this fleeting existence proved sufficient for Bose-Einstein condensation and the subsequent exhibition of superfluid behavior.
Theoretical predictions suggested the supersolid could settle into multiple equivalent states, and experimental results confirmed this expectation. “Theory predicted that the supersolid could choose among several equivalent states, and that is exactly what we observed,” said a researcher. This spontaneous selection of a state exemplifies spontaneous symmetry breaking, a fundamental concept in physics.
Beyond fundamental research, the demonstration of room-temperature supersolidity in exciton-polariton condensates opens possibilities for ultrafast photonic devices, neuromorphic computing and highly sensitive optical sensors, using the phase’s unique polarization sensitivity. This is the first time this combination of liquid-crystal microcavity and exciton-polariton condensate has been achieved, according to the researchers.
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
Liquid-Crystal Microcavities Enable Tunable Quantum State Exploration
The ability to manipulate the quantum state of matter electrically represents an advancement in the field, as demonstrated by a new platform using liquid-crystal microcavities. Researchers achieved this control by creating a supersolid within an exciton-polariton condensate, a feat previously limited to systems requiring extremely low temperatures. The team’s work suggests a future where quantum technologies can operate at temperatures far exceeding those previously thought possible, potentially accelerating the development of new optical devices.
We had to plan the entire sequence of experiments in advance.
Dr Marcin Muszyński, the paper’s first author, now a postdoctoral researcher at The City College of New York
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