Fig. 3. Comparison of the self-aligned sensors and nonaligned sensors prepared on a (100)-oriented diamond.

(A) The second-order correlation function g⁽²⁾(τ) (measured at an excitation power of ~40 μW) of the nonaligned devices with different photon counting rates. (B) The second-order correlation function g⁽²⁾(τ) (measured at an excitation power of ~40 μW) of the self-aligned devices with different photon counting rates. (C) Distribution of photon counting rate of NV sensors without alignment (at an excitation power of ~800 μW). (D) Distribution of photon counting rate of NV sensors by self-aligned (at an excitation power of ~800 μW). The black line is the Gaussian fitting to the data envelope, and the number of NV centers in the photonic device can be distinguished by the envelope. The inset shows the distribution of photon counting rate of a single NV sensor by self-aligned in an isotope-enriched diamond (¹²C 99.999%). (E and F) Histogram of the T₂ (Hahn echo pulse sequence) and T₂^*coherence time. The red and gray bars show the NV center sensors fabricated by self-alignment and without alignment, respectively. In addition, the inset shows the sensors fabricated by self-alignment in an isotope-enriched diamond (¹²C 99.999%) (G) The distribution of the number of NV in self-aligned devices obtained from (D) and fitted to a Poisson distribution. (H) The T₁ coherence time measurement. The red and gray points show the NV center sensors fabricated by self-alignment and without alignment, respectively.