Spectral analysis of amplitude-modulated microwave signals with nitrogen-vacancy centers in diamond

Microwave (MW) magnetometry utilizing nitrogen-vacancy (NV) centers in diamond offers a broad, tunable detection bandwidth enabled by the magnetic-field-dependent electron spin resonances (ESR) of the NV centers. In this work, we present and experimentally demonstrate two NV-based protocols for spectral analysis of amplitude-modulated (MW) signals. The first protocol employs the NV center as a band-pass filter and reconstructs frequency-domain information of MW signals by sweeping the MW carrier frequency. The second protocol achieves optical imaging of the MW spectrum using an NV-based quantum spectrum analyzer, wherein a magnetic field gradient spatially maps the ESR frequencies of the NV centers, enabling parallel detection of multiple spectral components over a wide instantaneous bandwidth. Both protocols show results that agree well with reference measurements from a classical spectrum analyzer. Our approaches extend the application of spin-based quantum sensors to the field of modern communications and can be adapted for other spin-based quantum sensors.