Simple Vector Magnetometer Based on Ground State Hanle Effect

We present a method for determining the azimuthal phase (angle) of a magnetic field by exploiting phase matching of laser beams in a ground-state Hanle effect (GHSE) configuration. This approach is based on the symmetry of the system’s Hamiltonian and the existence of a phase-independent frame, allowing for direct determination of the field orientation. As a proof of concept, we performed preliminary experiments using the Fg=1 to Fe=0 transition of the D2 line in 87Rb, with three laser beams to demonstrate the phase (azimuthal) dependence of the observed Hanle resonance signals. While our current setup does not include active phase control, the key features predicted by our method were observed, validating its conceptual foundation. Additionally, we measured two components of the stray magnetic field in our laboratory as an illustration. This method leverages the Hanle effect’s inherent sensitivity to both the magnitude and orientation of magnetic fields, as well as the underlying symmetry properties of the atomic system, and offers a pathway for precise, calibration-free determination of magnetic field orientation.