A supersolid is a rare and counterintuitive phase of matter that uniquely combines the rigidity of a crystal with the frictionless flow of a superfluid. “We can visualise it as a fluid made up of quantum coherent droplets periodically arranged in space, which are able to flow through an obstacle without undergoing perturbations, while maintaining their spatial arrangement and mutual distance unchanged as it happens in a crystalline solid”, said Iacopo Carusotto from the Pitaevskii BEC Center in Trento. While supersolidity has been explored in atomic Bose-Einstein condensates previously, this research represents the first experimental evidence of a supersolid phase in a driven-dissipative, non-equilibrium system using exciton-polaritons in a photonic crystal waveguide.
The researchers created the supersolid state by condensing polaritons in a bound-in-the-continuum state within a photonic crystal waveguide. The researchers were able to achieve remarkable precision in the measurement of density modulations, hallmark of translational symmetry breaking. At the same time, they probed the local coherence of the supersolid wavefunction.
“This is not merely a photonic analogy of atomic systems but a fundamentally new approach to achieving supersolidity”, said lead researcher Dimitrios Trypogeorgos. “This work not only demonstrates the observation of a supersolid phase in a photonic platform, but also paves the way for exploring quantum phases of matter in non-equilibrium systems,” said Daniele Sanvitto, group leader of the advanced photonic group at the CNR Nanotec in Lecce. “This is particularly significant because this approach has the potential to bridge the gap between fundamental science and practical applications,” he added.
“This work demonstrates the universality of this phase of matter, bringing new perspectives on what it takes to make a supersolid”, said Manuele Landini from the Department of Experimental Physics, who was actively involved in the work from its conception. This discovery has profound implications for the future of quantum technologies, including potential applications in neuromorphic computing and advanced photonic devices. The researchers are now exploring further opportunities to manipulate the supersolid state and investigate its low-energy excitation spectrum.
The research was a collaborative effort involving the CNR National Institute of Optics, the University of Pavia, and international institutions, including Princeton University, the Lawrence Berkeley National Laboratory, and the University of Innsbruck. The project received funding from several programs, including the National Quantum Science and Technology Institute (NQSTI) and the European Union.
Publication: Trypogeorgos, D. et al. Emerging supersolidity in photonic-crystal polariton condensates. Nature 2025 DOI: 10.1038/s41586-025-08616-9