Emerging supersolidity from a polariton condensate in a photonic crystal waveguide

TL;DR

This paper reports the first experimental observation of supersolidity in a polariton condensate within a photonic crystal waveguide, revealing spontaneous spatial self-organization and phase coherence in a non-equilibrium photonic system.

Contribution

It introduces a novel non-equilibrium supersolid phase realized with exciton-polaritons in a topologically non-trivial state, demonstrating spontaneous density modulation and phase coherence.

Findings

Observation of density modulation indicating broken translational symmetry

Measurement of local coherence of the superfluid component

Potential to host phonon dynamics and multimode excitation spectrum

Abstract

A supersolid is a counter-intuitive phase of matter where its constituent particles are arranged into a crystalline structure, yet they are free to flow without friction. This requires the particles to share a global macroscopic phase while being able to reduce their total energy by spontaneous, spatial self-organisation. This exotic state of matter has been achieved in different systems using Bose-Einstein condensates coupled to cavities, possessing spin-orbit coupling, or dipolar interactions. Here we provide experimental evidence of a new implementation of the supersolid phase in a novel non-equilibrium context based on exciton-polaritons condensed in a topologically non-trivial, bound-in-the-continuum state with exceptionally low losses. We measure the density modulation of the polaritonic state indicating the breaking of translational symmetry with a remarkable precision of a few parts in a thousand. Direct access to the phase of the wavefunction allows us to additionally measure the local coherence of the superfluid component. We demonstrate the potential of our synthetic photonic material to host phonon dynamics and a multimode excitation spectrum.