Resonance Tuning of Localized Excitons via a Plasmonic Nanocavity.

In monolayer semiconductors, excitons confined by strain-induced potential traps are promising candidates for on-chip single-photon sources. For these quantum emitters, achieving broadband tunability while preserving high brightness is crucial for quantum information processing and communication, but remains challenging in aligning the emitter energy with optical resonances. Here, we demonstrate resonant tuning of localized exciton emission in monolayer WSe using an Au nanocube-on-mirror nanocavity. The design enables simultaneous strain-induced exciton energy tuning and Purcell-enhanced emission. By adjusting the cavity gap, it allows precise spectral alignment of the localized exciton with the plasmonic resonance. We observe a record-large redshift over 240 meV in localized exciton energy. Compared with the conventional approach, a 22-fold enhancement in emission intensity is achieved due to the spectral, spatial, and polarization matching between the localized exciton and plasmons. Our findings establish a robust strategy for developing high-performance nonclassical light sources, facilitating the development of scalable quantum applications.