Three-axis isotropic-sensitivity He 4 magnetometer with alignment-based longitudinal parametric resonance

For measurements in near-zero magnetic fields, vector atomic magnetometers are promising alternatives to scalar versions, but generally suffer from inconsistent performance over three axes. We present a single-beam vector magnetometer with three-axis isotropic sensitivity based on He4 atomic alignment. Longitudinal parametric resonance with atoms pumped by linearly polarized light is proposed for the z-axis measurement, while the Hanle effect in transverse geometry is used for x- and y-axis measurements. The evolution of atomic alignment multipole components and expressions of the three-axis magnetic responses are analyzed in detail. We describe the experimental operation of the proposed magnetometer with a magnetic-field noise floor of 150fT/Hz1/2 for the three axes, which is attractive for biomagnetism requiring vector characterization and source reconstruction.