Figure 3: Optical characterization of NV-nanocavity systems.

(a) Photoluminescence confocal image of diamond PhC structures. The scale bar represents 5 μm. Single NVs are identified by circular white spots. System A: the dotted red circle shows a single NV close to the cavity centre (indicated by the blue dotted line). Inset: normalized second-order auto-correlation measurement with g⁽²⁾(0)=0.28. (b) Gas tuning of system A. The logarithmic plot shows the cavity resonance and two strain-split ZPL branches from a single NV (E_y and E_x, 2Δ=286 GHz, see Fig. 4a). As the gas condensation red shifts the cavity resonance, it sequentially enhances the two ZPL branches. The inset shows the intensity of the E_x ZPL transition as a function of cavity detuning. This curve follows the expected Lorentzian dependence of the Purcell enhancement given by equation 1, and shows that the cavity Q factor remains constant throughout the tuning process. (c) Spectra of system A in the uncoupled (I) and coupled cases with (II) and (III). Note the difference in scaling between E_x and E_y cases. The black lines are Lorentzian fits to the data, yielding Q=1,700±300 for the cavity. (d) System B at maximum Purcell enhancement. The inset shows a close-up of the spectrum. The ZPL transitions of four individual NVs (including the cavity-coupled ZPL) are visible, each with a different strain-induced spectral position. The accumulated phonon sidebands of these NVs are also apparent. (e) High resolution spectra of system B in cavity-coupled and uncoupled cases. The insets show the lifetime measurements corresponding to τ_on=6.7 ns and τ_off=18.4 ns. Norm., normalized.