DC Magnetic Field Sensitivity Optimization of Spin Defects in Hexagonal Boron Nitride

Spin defects existing in van der Waals materials attract wide attention thanks to their natural advantages for in situ quantum sensing, especially the negatively charged boron vacancy (V_B^-) centers in hexagonal boron nitride (h-BN). Here we systematically investigate the laser and microwave power broadening in continuous-wave optically detected magnetic resonance (ODMR) of the V_B^- ensemble in h-BN, by revealing the behaviors of ODMR contrast and line width as a function of the laser and microwave powers. The experimental results are well explained by employing a two-level simplified model of ODMR dynamics. Furthermore, with optimized power, the DC magnetic field sensitivity of V_B^- ensemble is significantly improved up to 2.87 ± 0.07 μT/$\sqrt{Hz}$. Our results provide important suggestions for further applications of V_B^- centers in quantum information processing and ODMR-based quantum sensing.