Sensitivity Improvement of DC and AC Magnetic Field Measurement Using NV Center via Frequency Modulation and Parameter Optimization

This article presents an experimental measurement scheme for direct current (DC) and alternating current (AC) magnetic fields based on optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in diamond. The work focuses on experimentally optimizing two established readout approaches on a custom platform rather than introducing a new ODMR mechanism. For DC magnetic field measurement, microwave frequency modulation combined with lock-in phase-sensitive demodulation is used to extract weak ODMR frequency shifts under magnetic-field perturbations. For AC magnetic field measurement, a Hahn echo quantum-control sequence is implemented, and the response of the NV centers to a 200 kHz AC signal is optimized by adjusting the free-evolution time. The results show that the platform can separately detect DC and AC magnetic fields with improved signal discrimination and robust responses under the tested conditions, providing experimental guidance for parameter selection in NV-center magnetometry.