Fig. 2: Optical properties of the single spin in hBN.

a 50 × 50-μm² confocal PL map of hBN arrays with 100-μW laser excitation at 532 nm. Our measurements correspond to the ultrabright single spin of Defect A circled in the image. b Room-temperature photoluminescence spectrum of Defect A under 532-nm laser excitation and with a 532-nm longpass filter. The zero-phonon line (ZPL) is indicated by green bands and the phonon sideband (PSB) is located at ~588 nm. c Second-order autocorrelation measurement g⁽²⁾(τ) of Defect A, which is measured at 100-μW laser power. The blue dots are the experimental data, the red curve is a fit based on the three-state model, and the yellow line represents g⁽²⁾(τ) = 0.5. Inset: A zoom of the same measurement for short timescales indicates the fitted g⁽²⁾(0) = 0.25 ± 0.02. d Emission (blue dots) polarization behaviors of Defect A. The red curve is fitted using a \({\cos }^{2}\theta\) function. e Saturation curve of Defect A under 532-nm laser excitation. “Corrected" means that the saturated intensity is corrected by the photon collecting and detecting efficiencies. See Supplementary Note 1. f Time-dependence of photoluminescence counts of Defect A, showing stable emission from Defect A.