Topological edge states of bound photon pairs

Abstract

We predict the existence of interaction-driven edge states of bound two-photon quasiparticles in a dimer periodic array of nonlinear optical cavities. The energy spectrum of photon pairs is dramatically richer than in the noninteracting case or in a simple lattice, featuring collapse and revival of multiple edge and bulk modes as well as edge states in continuum. We link the edge-state existence to the two-photon quantum walk graph connectivity. Our results offer a route to control quantum entanglement and provide insights into the physics of many-body topological states.