High-frequency resolution diamond NV center widespectrum imaging technology

Abstract

High-resolution wide-spectrum measurement techniques have significant applications in fields such as astronomy, wireless communication, and medical imaging. The nitrogen-vacancy (NV) center in diamond, known for its high stability, sensitivity, real-time monitoring, single-point detection, and suitability for long-term measurements, has become a prominent choice for spectrum analyzers. Currently, spectrum analyzers based on NV centers as detectors can perform real-time spectrum analysis within the range of several tens of gigahertz, but their frequency resolution is limited to the MHz level. In this study, we constructed a quantum diamond microwave spectrum imaging system combining continuous wave-mixing techniques. Leveraging the spin-related properties of the NV center in diamond, we employed optical pumping by illuminating the diamond NV center with 532 nm green laser light. A spherical magnet was used to apply a magnetic field gradient along one direction of the diamond crystal. By adjusting the size and direction of the magnetic field gradient, spatial encoding of the resonance frequency of the NV center was achieved. The magnetic field gradient induced the Zeeman effect on the diamond surface at different positions, resulting in corresponding ODMR signals. Through precise programming, we coordinated the frequency scanning step of the microwave source with the camera exposure and image storage time, cyclically synchronized according to the sequence for image acquisition. Ultimately, after algorithmic processing, we successfully obtained comprehensive spectrum data within the range of 900 MHz to 6.0 GHz. Within the measurable spectrum range, the system employed continuous wave-mixing, simultaneously applying resonant microwaves and slightly detuned auxiliary microwaves to effectively excite the NV center. This method triggered microwave interference effects, disrupting the balance between laser-induced polarization and microwave-induced spontaneous relaxation. Specifically, microwave interference caused changes in the phase and amplitude of the fluorescence signal, leading to the generation of alternating current fluorescence signals. This further enhanced the response of the NV magnetometer to weak microwave signals. The method enabled the system to achieve a frequency resolution of 1 Hz within the measurable spectrum range, and it could separately measure the frequency resolution of multiple frequency points with a 1 MHz frequency step. The research results indicate that wide-spectrum measurement based on NV centers can achieve sub-hertz frequency resolution, providing robust technical support for future spectrum analysis and applications.