Emitter–optomechanical interaction in ultrahigh-Q hBN nanocavities

A spectral anomaly exhibiting pronounced asymmetry is observed in the emission spectrum for nanocavities when they are pumped by the charged boron vacancy VB− and have a high Q-factor above a threshold of 10 000. In contrast, cavities without VB− centers always exhibit trivial Lorentzian emission. These observations are well explained by the feature of VB− that its light–matter interaction is induced by local phonon modes. Moreover, we find that in nanocavities the local phonon modes arise from the coupling between VB− lattice phonons and cavity mechanical modes, supported by the spatially resolved spectroscopy of VB− and resonant spectroscopy of the cavity photonic mode. Our results reveal a novel system involving the coupling in both the photonic and phononic degrees of freedom between the active material and the nanocavity. Such an emitter–optomechanical interaction system shows great potential in non-trivial quantum photonic devices and provides a platform to interface spin defects, photons, and phonons.