Topological matter and topological optics have been studied in many systems, with promising applications in materials science and photonics technology. These advances motivate the study of the interaction between topological matter and light, as well as topological protection in light-matter interactions. In this work, we study a waveguide-interfaced topological atom array. The light-matter interaction is nontrivially modified by topology, yielding optical phenomena. We find topology-enhanced photon absorption from the waveguide for a large Purcell factor, i.e., $\mathrm{\Gamma }/{\mathrm{\Gamma }}_0\gg 1$, where $\mathrm{\Gamma }$ and ${\mathrm{\Gamma }}_0$ are the atomic decays to the waveguide and environment, respectively. To understand this unconventional photon absorption, we propose a multichannel scattering approach and study the interaction spectra for edge- and bulk-state channels. We find that, by breaking inversion and time-reversal symmetries, optical anisotropy is enabled for the reflection process, but the transmission is isotropic. Through a perturbation analysis of the edge-state channel, we show that the anisotropy in the reflection process originates from the waveguide-mediated non-Hermitian interaction. However, the inversion symmetry in the non-Hermitian interaction makes the transmission isotropic. At a topology-protected atomic spacing, the subradiant edge state exhibits huge anisotropy. Because of the interplay between edge- and bulk-state channels, a large topological bandgap enhances nonreciprocal reflection of photons in the waveguide for weakly broken time-reversal symmetry, i.e., ${\mathrm{\Gamma }}_0/\mathrm{\Gamma }\ll 1$, producing complete photon absorption. We show that our proposal can be implemented in superconducting quantum circuits. The topology-enhanced photon absorption is useful for quantum detection. This work shows the potential to manipulate light with topological quantum matter.

• Received 17 August 2020
• Revised 23 February 2021
• Accepted 30 March 2021

DOI:https://doi.org/10.1103/PhysRevApplied.15.044041