In Situ Synchronous Measurement of Low-Frequency Magnetic Field Fluctuation Based on Temporal Differencing in Atomic Comagnetometer

Fluctuations in transverse low-frequency magnetic fields significantly impact the long-term stability of atomic comagnetometers (ACMs). Due to the strong coupling between magnetic fields and gyro signals, conventional evaluation approaches are typically limited to offline analysis. To address this challenge, this article proposes a temporal differencing (TD) technique combined with baseline alignment (BA), leveraging quantum spin dynamics under longitudinal magnetic field modulation to construct a differential response model. The TD approach compresses the response time scale of the system, thereby enhancing immunity to multisource disturbances. Meanwhile, BA enables the synchronous acquisition of magnetic field fluctuations and gyro signals, facilitating real-time evaluation. Experimental results show that under disturbances such as probe light power, pump light power, and vapor cell temperature, the proposed TD method achieves a suppression of at least 56.5% compared with induced nuclear spin resonance (INSR) and a suppression of at least 65.6% compared with the Z-mode method, covering all components of the transverse field. Furthermore, the equivalent angular velocity deviations caused by transverse field fluctuations are quantified as $6.9 \times {10}^{-3}$ °/h along the x-axis and $2.9 \times {10}^{-3}$ °/h along the y-axis, contributing 28.4% and 11.9% to the degradation of the long-term stability of the ACM, respectively. These results demonstrate that the proposed method enables accurate and reliable in situ evaluation of transverse magnetic field disturbances and offers practical insights for enhancing the robustness of ACM systems.