Magnetic Field Sensitivity Optimization of Negatively Charged Boron Vacancy Defects in hBN.

Optically active spin defects in hexagonal boron nitride (hBN) have recently emerged as compelling quantum sensors hosted by a two dimensional (2D) material. The photodynamics and sensitivity of spin defects are governed by their level structure and associated transition rates. These are, however, poorly understood for spin defects in hBN. Here, optical and microwave pump-probe measurements are used to characterize the relaxation dynamics of the negatively charged boron vacancy (V-B(-))-the most widely-studied spin defect in hBN. A 5-level model is used to deduce transition rates that give rise to spin-dependent V-B(-) photoluminescence, and the lifetime of the V-B(-) intersystem crossing metastable state. The obtained rates are used to simulate the magnetic field sensitivity of V-B(-) defects and demonstrate high resolution imaging of the magnetic field generated by a single magnetic particle using optimal sensing parameters predicted by the model. The results reveal the rates that underpin V-B(-) photodynamics, which is important for both a fundamental understanding of the V-B(-) as a spin-photon interface and for achieving optimal sensitivity in quantum sensing applications.