Our new paper, Close Encounters between Periodic Light and Periodic Arrays of Quantum Emitters, has been published in Physical Review Letters!

In this work, we introduce crystal polaritons, hybrid light-matter excitations formed when collective excitations of a periodic array of quantum emitters strongly couple to the Bloch modes of a metasurface. This provides a new cavity-QED platform in which periodic light and periodic matter are treated on equal footing.

To describe this regime, we develop a reciprocal-space few-mode quantization approach based on macroscopic quantum electrodynamics. It maps the resonances of a general, lossy, and dispersive metasurface onto a cavity-QED Hamiltonian at every in-plane momentum. We show that both plasmonic surface-lattice resonances and dielectric bound states in the continuum can achieve strong coupling with only one emitter per unit cell.

The resulting crystal polaritons inherit strong resonant nonlinearities, enabling quantum-light generation with efficiencies orders of magnitude greater than conventional nonlinear metasurfaces. The work was done in collaboration with Frieder Lindel, Carlos J. Sánchez Martínez and Francisco J. García Vidal.