Topologically protected strong photon-exciton coupling

We propose that strong photon-exciton coupling performed by a plasmonic nanoantenna and a single emitter can be protected in the well-designed topological photonic structure as an environment. Topological robustness leads to a reduction of metal loss, which makes Rabi splitting much larger. The strong coupling regime gets more stable in the topological systems because the sensitivity characterized by Rabi splitting can always remain small compared to the sensitive nontopological systems. Moreover, we show that the Rabi splitting under topological protection is immune to defects or impurities that can destroy strong coupling in nontopological systems. This topologically protected strong coupling mechanism offers more improvement in the applications of on-chip quantum integration, single quantum sources, and quantum information processing.