Rapid atomic-signal-based <i>in-situ</i> magnetic compensation for unshielded spin-exchange relaxation-free atomic magnetometer

We propose a novel method, which leverages the atomic signal itself, to achieve rapid in situ magnetic field compensation in an unknown geomagnetic environment for an unshielded spin-exchange relaxation-free atomic magnetometer. This method employs a strong bias magnetic field aligned with the pump beam direction to maximize the strength of the magnetic field resonance signal. The compensation process is divided into three sequential stages, each focusing on one of the x, y, and z axes by adjusting the magnitude of the bias magnetic field. As a result, the zero magnetic field is identified within 11 seconds, with compensation resolution smaller than 3.0 nT, primarily constrained by the laser power stability. This approach not only enhances the applicability of atomic magnetometers in unshielded environment but also proves effective for in situ magnetic field compensation in shielded environment, such as those used in magnetoencephalography, magnetocardiography, and space science.