High robustness of NV sensors in diamond using hybrid heterodyne technique for audio recognition

Abstract

Importance of using nitrogen-vacancy (NV) center as quantum sensors in diamonds is of great significance in their high sensitivity and stability, which are widely applied in microwave detection area. Especially, the heterodyne technique can beyond the limitation of quantum coherence time and stands out with the advantage of high frequency resolution. However, the realization of high frequency resolution relies on long-time measurements, so how to reduce the noise and maintain the stability of the system during the long-time measurements has become an urgent problem. Here, we propose a novel method for NV sensors that combines common-mode rejection (CMR) and proportional and integral (PI) control techniques with the heterodyne technique. This method achieves a 5 dB increase in signal-to-noise ratio (SNR) and measurement stability over long periods of time with 2.4 times improvement in the minimum Allan variance averaging time. Where, the CMR and PI technologies achieve high SNR and longtime stability by matching the differential inputs to reduce the common mode noise and by decreasing steady-state error through an integral controller, respectively. A frequency resolution of 9.5 mHz and the minimum detectable magnetic field of 4.85pT over an average time of ≈2400 s have been achieved by using the hybrid heterodyne technique. Finally, we demonstrate the capability of audio recognition with this hybrid heterodyne technique, as well as having potential application in fields such as magnetic resonance imaging (MRI) and unknown signal exploration.