Zero‐Position Closed‐Loop Control of Nuclear Spin in a K‐Rb‐21Ne$^{21}{\rm Ne}$ Comagnetometer

Abstract In SERF (spin‐exchange relaxation‐free) comagnetometers, the fluctuation of the atomic ensemble's polarization significantly impacts the long‐term stability of the output signal. A real‐time closed‐loop control method for the nuclear spin polarization is proposed, and the measurement model is established using Kalman state observer. Furthermore, magnetic field control signals are generated using a proportional‐integral‐derivative (PID) strategy, which is then applied to the atomic ensemble to dynamically adjust the nuclear spin polarization. Finally, closed‐loop control of nuclear spin polarization is achieved through continuous feedback and control. Moreover, experiments have demonstrated that implementing a closed‐loop system for nuclear spin zero‐position is conducive to reducing the sensitivity of the output signal to fluctuations in the external environment. The experimental results show that the Allan deviation at 100 s is reduced by , and the sensitivity of inertial rotation measurement is significantly improved, that is, the noise level at 1 Hz is suppressed by approximately .