Coherent Dynamics of Strongly Interacting Electronic Spin Defects in Hexagonal Boron Nitride

Optically active spin defects in van der Waals materials are promising platforms for modern quantum technologies. We investigate the coherent dynamics of strongly interacting ensembles of negatively charged boron-vacancy (V_B^-) centers in hexagonal boron nitride (hBN) with varying defect density. By employing advanced dynamical decoupling sequences to selectively isolate different dephasing sources, we observe more than 5-fold improvement in the measured coherence times across all hBN samples. Crucially, we identify that the many-body interaction within the V_B^- ensemble plays a substantial role in the coherent dynamics, which is then used to directly determine the precise concentration of V_B^-. We find that at high ion implantation dosage, only less than 5 % of the created boron vacancy defects are in the desired negatively charged state. Finally, we investigate the spin response of V_B^- to the local charged defects induced electric field signals, and estimate its transverse electric field susceptibility of V_B^-. Our results provide new insights on the spin and charge properties of V_B^-, which are important for future use of defects in hBN as quantum sensors and simulators.