Fig. 2: Spin- and charge-state stability of the deep NV center.

a Average fluorescence under optical pumping with a 637 nm laser being resonant to the main |0〉 transition. In the upper panel, the NV center was initialized to |0〉 with (70 ± 1)% probability by a simple green laser pulse, followed by no MW excitation (blue) or by a π-pulse on either the |0〉 ↔ |+1〉 or |0〉 ↔ |−1〉 transition (magenta and green curve). The lower panel displays the same measurement after initializing to |+1〉 with (88 ± 2)% probability using the explicit spin initialization protocol presented in Fig. 1c. The insets are sketches of the sequence used for the upper and lower panels. b Charge-state stability under excitation with the 637 nm laser plus cw MW excitation at both ground-state MW transitions. This was alternated with 1 s of green repumping. These data are not averaged, but just one repetition. c Average fluorescence of the NV being preferentially in the charge states NV⁻ (upper curve) or NV⁰ (lower curve). These data (without using postselection) were taken simultaneously with the data presented in d. d Distribution of the number of fluorescence photons that were detected during 1 ms of readout. The upper panel displays the distribution directly after the charge-state initialization to NV⁻, as shown in Fig. 1c, while the lower part includes a strong ionization pulse in between initialization and readout for conversion to NV⁰. The dotted line indicates the threshold used for analysis. Note the logarithmic y scale.