Topological edge states of bound photon pairs

TL;DR

This paper predicts interaction-driven topological edge states of bound photon pairs in nonlinear optical cavity arrays, revealing complex spectral features and linking their existence to quantum walk graph connectivity.

Contribution

It introduces the concept of topological edge states for bound photon pairs in nonlinear lattices and connects their existence to quantum walk graph connectivity.

Findings

Photon pair spectrum shows collapse and revival of edge and bulk modes.

Edge states exist in continuum despite breakdown of Zak phase technique.

Topological nature linked to two-photon quantum walk graph connectivity.

Abstract

We predict the existence of interaction-driven edge states of bound two-photon quasiparticles in a dimer periodic array of nonlinear optical cavities. 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. Despite the unexpected breakdown of the Zak phase technique and the edge mixing of internal and center-of-mass motion we link the edge state existence to the two-photon quantum walk graph connectivity, thus uncovering the topological nature of the many-body problem in complex lattices.