Nanoscale Spin Cross-Relaxometry between Diamond NV Centers and 2D Spin Defects

Spin defects in solids provide long-lived quantum states ideal for sensing and information storage. We integrate a single nitrogen-vacancy (NV) center in diamond with scanning probe microscopy to discover, read out, and spatially map nanoscale spin-based quantum sensors. Using the boron vacancy (VB−) center in hexagonal boron nitride as a model system, we indirectly detect its electron spin resonance by monitoring changes in the NV center’s spin relaxation time (T1), eliminating the need for optical excitation or fluorescence detection of VB−. Cross-relaxation between NV and VB− ensembles significantly shortens NV T1, enabling quantitative mapping of defect densities beyond the optical diffraction limit and resolving hyperfine splitting in isotopically enriched h10B15N. Our approach demonstrates robust interactions between 3D and 2D spin sensors, establishing NV centers as versatile probes to characterize otherwise inaccessible spin defects.