Self-ordering of individual photons in waveguide QED and Rydberg-atom arrays

The scattering between light and individual saturable quantum emitters can induce strong optical nonlinearities correlations quanta. Typically, this leads to an effective attraction that generate exotic bound states of photons, which form mechanical precursors solitons, as found in many media. Here, we study the propagation through waveguide is chirally coupled three-level emitters. We show additional laser-coupling a third emitter state not only permits control properties but even eliminate it entirely. This makes possible turn otherwise focussing nonlinearity into repulsive photon-photon interaction. demonstrate emerging repulsion by analysing dynamics multiple photons large arrays reveal dynamical fragmentation incident uncorrelated fields self-ordering regular trains single photons. These striking effects expand rich physics electrodynamics domain establish conceptually simple platform explore self-organization phenomena at level. discuss implementations setting cold-atom experiments propose new approach based on mesoscopic Rydberg-atom ensembles.