Fig. 2: Characterization of the optical interface of the cavity-coupled NV center.
a PLE measurement of the NV center’s Ey transition (readout transition) in the LF cavity mode with a Gaussian fit (solid line) and a full width at half maximum (FWHM) linewidth. The background-corrected (bg-corr.) zero-phonon line (ZPL) counts are plotted over the excitation laser frequency with respect to (w.r.t.) 470.4 THz. Details about the PLE measurement sequence and the applied background correction are presented in Supplementary Note 2. b Pulsed resonant saturation measurement of the readout transition in the LF cavity mode, together with a linear fit as a guide for the eye. The probability (prob.) of a ZPL detector click is plotted over the laser pulse peak power. The inset shows the time-resolved detector counts for a laser pulse peak power of 35 μW measured free-space before the objective and the used integration window from 3 ns to 30 ns with respect to the excitation pulse center. The small peak at a detection time of about −5 ns is light of the excitation pulse that is backscattered into the free-space detection before reaching the cryostat. c Lifetime measurements of the NV center’s Ey excited state on cavity resonance in the LF and HF cavity modes, as well as off resonance in the LF mode. Details about the applied background correction are outlined in Supplementary Note 4. The fit windows of 5 ns to 18 ns are represented by the length of the solid lines of the monoexponential fits. The data is normalized (norm.) and offset for visual clarity. d Second-order correlation measurement of the readout transition in the LF cavity mode for a pulse train of 30 consecutive short resonant excitation pulses. In this measurement, the integration window of (b) is used. The triangular function capturing the finite pulse train (black dashed line) is shown next to the fit function that also includes the spin flipping process (black solid line).
