Credit: Light: science & applications
(a, b) Single-photon chiral outer edge state and inner edge state (IEB, IEA) are transferred from input sites (pink dots) to output sites (yellow dots) in the one-period lattice, as shown in the left. The red, blue, and green arrows represent the unidirectional topological transport of single-photon outer edge, inner edge IEA, and inner edge IEB states, respectively. The quantum interference curves and visibilities V are shown in the right.