Subradiant bound dimer excited states of emitter chains coupled to a one dimensional waveguide

This article shows that chains of optical or microwave emitters coupled to a one-dimensional (1D) waveguide support subradiant states with close pairs of excited emitters, which have longer lifetimes than even the most subradiant states with only a single excitation. Exact, analytical expressions for nonradiative excitation dimer states are obtained in the limit of infinite chains. To understand the mechanism underlying these states, we present a formal equivalence between subradiant dimers and single localized excitations around a chain defect (unoccupied site). Our analytical mapping permits extension to emitter chains coupled to the 3D free space vacuum field.