Fig. 1: ODMR persistence with applied magnetic field.

a Schematic of the hBN layers containing a spin defect with in-plane spin principal axis. 3D model of the crystalline structure was generated using ref. ⁶⁷. b Spatial photoluminescence (PL) map of a hBN device containing individually addressable defect centres. c PL spectrum of the carbon-related defect in hBN. d Schematic of the electronic level structure of the defects, consisting of ground and optically excited-state manifolds, and a metastable state. Relaxation from the optically excited-state to the ground-state manifold can occur radiatively (solid orange arrow) or non-radiatively (dashed grey arrows) through a sequence of direct and reverse intersystem crossing events. The ground-state manifold is a spin-1 with non-degenerate spin sublevels at zero magnetic field. Spin-resonance transitions between each of the three spin sublevels are possible, giving rise to three spin-resonance signatures, labelled f_A,B,C in ascending energy. e cwODMR spectra measured at 0 mT (top panel) and 51(1) mT (bottom panel), showing three spin transitions between the spin sublevels of an S = 1 system. Blue circles are measured mean values, with grey error bars indicating the standard error of the mean. Shaded regions are fits to the data using a Gaussian peakshape. The inset in the top panel presents the pulse sequence used for detecting cwODMR, whereas the inset in the bottom panel presents the direction of the magnetic field with respect to the defect’s symmetry axes.