Quantum materials made of light

Can strongly correlated materials be built out of light? Certainly not with ordinary photons, which freely propagate at the speed of light and do not interact with each other at all. However, I will explain how we turn photons into strongly-interacting cavity Rydberg polaritons, quasiparticles which are confined to the modes of an optical cavity and gain strong interactions from Rydberg excitations of an atomic gas. Once they have been imbued with these key properties, photons naturally form strongly correlated matter. In fact, we have recently observed the formation of photon pairs in the Laughlin state, the paradigmatic example of topological order which underlies the fractional quantum Hall effect in electron gases. We characterize these entangled Laughlin "puddles" by measuring photon-photon correlations in both real space and angular momentum space, exemplifying the unique and powerful new perspective that many-body quantum optical systems can provide for illuminating quantum matter.