• In a major breakthrough, scientists have successfully “frozen” light, demonstrating that it can behave as a supersolid — a rare state of matter that exhibits both solid-like structure and frictionless flow.

• It marks a significant milestone in quantum physics and could revolutionise future applications in quantum computing and optical technologies.

• The scientists demonstrated the emergence of a supersolid phase of matter in a photonic crystal polariton condensate. 

• This pioneering work, published in Nature, introduces a new platform for exploring supersolidity beyond traditional ultracold atomic systems.

What is supersolid?

• 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.

• It can be visualised 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.

• The existence of the supersolid phase of matter was speculated more than 50 years ago. However, only recently has there been convincing experimental evidence, mainly using ultracold atomic Bose–Einstein condensates (BECs) coupled to electromagnetic fields.

• 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 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.

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