Imaging Frequency-Modulated Microwaves Using a Robust Quantum Spectrum Analyzer

Spin-based quantum sensors have been applied to the quantum sensing of magnetic fields from DC to GHz with various schemes. The recently developed quantum spectrum analyzer (QSA) technique based on the nitrogen-vacancy (NV) centers in diamond shows an ultrawide frequency bandwidth in this application. Here, we improve this technique and develop a robust QSA via diamond engineering. This QSA exploits the electron spin resonance of NV centers in an engineered {111} industrial diamond, which cancels the complex process of magnetic arrangement and significantly enhances the robustness of QSA against spin mixing under high magnetic fields in practice. A tunable frequency bandwidth of up to 18 GHz with a maximum instantaneous bandwidth of 2 GHz is achieved as well as a frequency resolution of several MHz and a large dynamic range of 65 dB. Using this QSA, we realize the optical imaging of frequency-modulated microwaves. Our work provides a promising rapid-deployment architecture for QSA and extends its application to spectral analysis in modern communications.