Nitrogen-vacancy (NV) centers, typical luminescent point defects in diamond with excellent spin properties, have been widely used to characterize physical quantities such as magnetic field, electric field, and temperature, which not only provide scientists with a new tool for exploring and understanding physical phenomena but also open up a new path for the development of quantum sensing technology. Significant progress has been made in quantum sensing platforms based on NV centers in recent years. In medicine, this technology offers the possibility of non-destructive and non-invasive bio-imaging and diagnostics. Geologists use NV centers to probe the physical properties of the Earth's interior, NV centers provide new means for geological exploration and resource exploitation. In industrial inspection, NV centers-based sensors also provide more accurate measurements for product quality control and process optimization. With further research and technological development, NV centers-based quantum sensing platforms will play an even more important role in the future, opening the door to a deeper understanding of the natural world.

Measurements with high resolution and sensitivity are essential in the field of weak magnetic detection. It is because weak magnetic field changes often hide in a large amount of background noise, which makes it difficult to be accurately captured. Actually, NV centers-based magnetometers face a lot of noise interference in real measurements, which seriously affects the purity of the measured signal and leads to biased judgment of the real signal. For more accurate detection of weak magnetism, it is necessary to thoroughly study the noise sources of NV centers-based magnetometers and explore effective noise reduction methods to improve their measurement resolution and sensitivity.

To solve the above problems, the Laser Physics and Quantum Modulation team from the School of Physics of East China University of Science and Technology introduces a compound filter system combining a wavelet denoising method and an adaptive filter to enhance the signal-to-noise ratio (SNR) of NV diamond magnetometry in Chinese Optics Letters Vol. 21, Issue 11, 2023: An Ye, Dingyuan Fu, Mingming Wu, Jiahao Guo, Tianze Sheng, Xiaolin Li, Shangqing Gong, Yueping Niu. SNR enhancement of magnetic fields measurement with the diamond NV center using a compound filter system[J]. Chinese Optics Letters, 2023, 21(11): 111201.

Traditional differential methods are used in the processing of signals, but they are primarily aimed at low-frequency noise cancellation, and as application requirements continue to expand, the elimination of the low-frequency portion of the noise is not sufficient to meet the needs of a wider range of applications. An Ye, a doctoral student who carried out this work, describes the starting point of the work, "SNR optimization for NV centers-based magnetic measurements has mainly focused on signal amplitude enhancement, and there is also great potential to improve system performance if we work on noise processing.". Based on this understanding, this work further processes the signal by combining the wavelet denoising method and the adaptive filtering technique to further eliminate the noise in the high-frequency part, which offers a new way to solve the inadequacy of the traditional differential method in high-frequency noise processing.

In this work, the wavelet denoising method is first used to finely disassemble the measurement signal into different high-frequency and low-frequency components, and the noise is removed while the signal features are greatly preserved by setting an appropriate threshold. To further highlight the signal characteristics, an adaptive filtering technique based on the variable step factor is designed, which avoids the limitations that may be brought by the fixed parameters. By dynamically adjusting the filter parameters, the optimal filtering effect is continuously maintained without the need to give a priori information, and thus the SNR is finally successfully improved in low-frequency and weak magnetic environments, which more effectively meets the challenges of measurements in complex magnetic field environments.

Confronted with the diversity of application environments, NV centers-based magnetometers will face more challenges and opportunities, but they also need to have more comprehensive performance, not only to eliminate low and high-frequency noise but also to be able to adapt to a variety of complex signal environments. In the future, the team will also continue to explore and innovate to develop more advanced and efficient signal processing methods and techniques to meet the growing application needs.

Schematic of the experimental setup. The inset depicts the detailed section for NV sensing.