Near-zero-field magnetometers, particularly the spin-exchange relaxation-free (SERF) magnetometer, despite their exceptional sensitivity, face a fundamental limitation: their accuracy is inherently tied to the precision of precalibrated magnetic coils, creating a circular dependency in calibration. To break this loop, we establish a comprehensive analytical framework to describe the full-sequence free-induction-decay (FID) trajectories of atomic ensembles in the near-zero magnetic field regime. By explicitly incorporating the dynamic evolution of the polarization-dependent slowing-down factor $q(P)$, our model provides a rigorous description of spin precession in ultraweak field environments, enabling the extraction of absolute field components without relying on external coil-based references. The mathematical integrity of the model is confirmed by excellent agreement with direct numerical simulations of the Bloch equations. We demonstrate that a single FID waveform can simultaneously resolve six independent physical parameters through a multiparameter nonlinear estimation process. Experimental results validate that the reconstructed magnetic fields exhibit high fidelity, with a coefficient of determination of approximately 0.99. Under current experimental conditions, this approach achieves a practical reconstruction uncertainty of 0.1 nT for the absolute magnetic field and 5 and $1{\mathrm{s}}^{-1}$ for pumping and relaxation rates, respectively. This work redefines the SERF magnetometer as a calibration-free magnetometer, providing a robust foundation for autonomous quantum sensing in remote or inaccessible environments.

Close

PrevNext

View figure in article

• Magnetometry
• Optical pumping
• Quantum measurements
• Quantum sensing
• Spin dynamics
• Spin polarization
• Alkali metals
• Atomic gases