Simultaneous in-situ compensation method of residual magnetic fields for the dual-beam SERF atomic magnetometer

Near-zero magnetic field condition is essential to keep the spin-exchange relaxation-free (SERF) regime for the atomic magnetometer. We analyzed the output response variations of the dual-beam SERF magnetometer under different DC residual magnetic fields. Considering the problem that the gradient coil may introduce an additional DC magnetic field when compensating the gradient field, we propose a novel method of simultaneous in-situ compensation of gradient and DC residual magnetic field with high precision. The sensitivity and effectiveness of the compensation method for residual magnetic fields under 1 nT were verified by simulation and experiment. The precision of the gradient residual magnetic field compensation is better than 2 pT/mm. We built a dual-beam SERF atomic magnetometer platform to validate the proposed method. The magnetic field measurement sensitivity is 7 fT/Hz^1/2 after residual magnetic fields compensation by the method mentioned in this paper, which is 4 times higher than the sensitivity of 36 fT/Hz^1/2 without residual magnetic fields compensation.