Recently, the quantum precision measurement research team achieved significant progress in extremely low-frequency magnetic field detection. By leveraging the nonlinear response characteristics of diamond NV color center ensemble magnetometers, the team successfully achieved a significant improvement in the signal-to-noise ratio (SNR) of extremely low-frequency (less than 10 Hz) magnetic field signals. The research results were published in Advanced Optical Materials under the title "Enhancing Extremely Low-Frequency Signal-to-Noise Ratio of Diamond Magnetometry via Nonlinear Response" (DOI: 10.1002/adom.202501340).

Figure 1: (a) Diamond sensor fabricated for chip detection using ion implantation; (b) The charge state characteristics of the diamond color center sensor revealed; (c) Ultra-high sensitivity and resolution of spin-based quantum magnetic field detection achieved.

Extremely low-frequency magnetic field detection has important applications in high-voltage DC systems, lithium-ion battery diagnostics, and industrial process monitoring. However, conventional magnetometers often face challenges with low-frequency noise interference and insufficient sensitivity when detecting extremely low-frequency signals. The team innovatively proposed a method combining a flux concentrator with a nonlinear response, successfully extending the magnetic field detection bandwidth to the hertz range while significantly improving detection sensitivity. The team designed a "connected" flux concentrator structure that amplifies weak current signals using high-permeability materials, driving the NV color center ensemble into the nonlinear response region of the optically detected magnetic resonance (ODMR) differential spectrum, as shown in Figure 1. Within this region, the nonlinear effect not only enables signal frequency mixing but also significantly suppresses 1/f low-frequency noise. Experimental results show that for a 0.5 Hz signal, the signal-to-noise ratio is improved by 2.6 times, enabling clear extraction of signals previously obscured by low-frequency noise. The innovation of this research lies in the simultaneous noise suppression and signal demodulation achieved through the nonlinear response mechanism, providing a new strategy for extremely low-frequency magnetic field detection. This method is not only applicable to current magnetic field detection but can also be extended to geomagnetic sensing, biomagnetic field detection, and low-frequency magnetic resonance measurements, offering broad application prospects.

Hefei University of Technology is the first affiliation of the paper. Chunlong Li, a postdoctoral researcher, is the first author of the paper. Renfei Zheng, Professsor Chen, and Professor Xue are co-corresponding authors. Master's student Hao Wu undertook important work in the early stages of the project, including the design of the flux concentrator and the construction of the optical path. This research was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Anhui Provincial Science and Technology Key Project, and the Fundamental Research Funds for Central Universities.

Renfei Zheng (Figure and text), Weiqing Gao (Reviewed)