In-situ Measurement of Residual Magnetic Field in a SERF Comagnetometer Based on Polarization Reversal

This paper introduces an in-situ method for measuring residual magnetic fields in spin-exchange relaxation-free (SERF) comagnetometers using the nuclear polarization reversal. Residual magnetic fields reduce the effectiveness of compensation coils and weaken the system's resilience to magnetic disturbances, ultimately degrading measurement accuracy. Therefore, accurate quantification of the residual magnetic field inside magnetic shields is essential for optimizing comagnetometer performance. Conventional methods primarily target the transverse field components or require intrusive hardware modifications. Our approach exploits steady-state nuclear polarization dynamics under left-and right-handed circularly polarized pumping. We achieved the reversal of both electron and nuclear spin polarization, and performed magnetic field zeroing before and after each reversal. The longitudinal residual magnetic field was then accurately obtained from the difference in compensation fields. Experimental validation on a K-Rb-21Ne SERF comagnetometer yielded a residual field measurement of (1.06 ± 0.09) nT with 0.06 nT resolution. Compared to using an extra magnetometer for residual field measurement, this in-situ approach offers higher accuracy without altering the original operating conditions of the magnetically shielded system.