In Situ Closed‐Loop Control of Polarization via Dual‐Axis Magnetic Field Modulation

ABSTRACT

This paper addresses the issue of susceptibility to longitudinal magnetic field interference in in situ closed‐loop polarization control and introduces an innovative in situ closed‐loop control method for electronic longitudinal polarization via dual‐axis magnetic field modulation. This approach effectively suppresses interference from the longitudinal magnetic field and significantly enhances system stability. By varying the pump rate and analyzing the system's response characteristics, it is observed that, under dual‐axis magnetic field modulation, changes in electron polarization and the longitudinal magnetic field notably influence the amplitude‐frequency response of the system output. Both theoretical derivations and experimental results show that using the calculated amplitude‐frequency response of the system output, as calculated, as a feedback signal enables real‐time in‐situ closed‐loop control of electron spin polarization. Compared to the traditional single‐axis magnetic field modulation approach, this method offers substantial advantages in mitigating noise interference. Compared with the conventional method, the noise amplitude spectral density of the proposed method at 0.1 Hz is improved from 0.0004098 to 0.000129. This technique holds considerable promise for a wide range of applications, including optical pumping magnetometers, nuclear magnetic resonance gyroscopes, and various co‐magnetometer systems.