Accurate vector optically pumped magnetometer with microwave-driven Rabi frequency measurements

TL;DR

This paper presents a highly accurate vector optically pumped magnetometer that uses microwave-driven Rabi frequency measurements to improve calibration, reduce systematic errors, and achieve sub-degree accuracy in magnetic field detection.

Contribution

The study introduces a novel Rabi measurement technique using dressed-state resonances and demonstrates a microfabricated vapor cell sensor with unprecedented vector accuracy and sensitivity.

Findings

Achieved average vector accuracy of 0.46 mrad.

Demonstrated vector sensitivity down to 11 μrad/√Hz.

Surpassed 1-degree accuracy threshold of existing OPMs.

Abstract

Robust calibration of vector optically pumped magnetometers (OPMs) is a nontrivial task, but increasingly important for applications requiring high-accuracy such as magnetic navigation, geophysics research, and space exploration. Here, we showcase a vector OPM that utilizes Rabi oscillations driven between the hyperfine manifolds of $^{87}$Rb to measure the direction of a DC magnetic field against the polarization ellipse structure of a microwave field. By relying solely on atomic measurements -- free-induction decay (FID) signals and Rabi measurements across multiple atomic transitions -- this sensor can detect drift in the microwave vector reference and compensate for systematic shifts caused by off-resonant driving, nonlinear Zeeman (NLZ) effects, and buffer gas collisions. To facilitate dead-zone-free operation, we also introduce a novel Rabi measurement that utilizes dressed-state resonances that appear during simultaneous Larmor precession and Rabi driving (SPaR). These measurements, performed within a microfabricated vapor cell platform, achieve an average vector accuracy of 0.46 mrad and vector sensitivities down to 11 $\mu$rad$/\sqrt{\text{Hz}}$ for geomagnetic field strengths near 50 $\mu$T. This performance surpasses the challenging 1-degree (17 mrad) accuracy threshold of several contemporary OPM methods utilizing atomic vapors with an electromagnetic vector reference.