Enhancing the Ramsey contrast of an NV-ensemble in diamond using quantum optimal control

Abstract Negatively charged nitrogen-vacancy (NV) centers in diamonds are commonly used in quantum magnetometry. However, the potential of this approach is often limited by the inhomogeneity of the driving field. In this study, we explore the potential of closed-loop quantum optimal control to improve DC Ramsey magnetometry with NV-ensembles suffering from inhomogeneous microwave (MW) fields and MW power limitations. We demonstrate an improvement of the optically detected Ramsey contrast up to a factor of 3.13. This enables noticeable power savings for miniaturized devices without loss in magnetometry performance. Additionally, we show a recovery of 86.3% of the Ramsey contrast in presence of a five times less homogeneous MW field compared to the homogeneous field of a MW Helmholtz coil pair.