Optically-pumped magnetometers (OPMs) are widely used for their scalar sensitivity, accuracy, and compact sensor packages, but require additional mechanical references for vector magnetometry. These mechanical references, such as a coil system, often limit the vector accuracy due to machining tolerances and drifts. Current approaches to improve vector accuracy are calibrations that involve physical rotations of the magnetometer system at the expense of increasing the complexity of the physical apparatus. In this poster we demonstrate Rabi magnetometry as a novel approach to vector sensing with an OPM that utilizes a microwave polarization ellipse (MPE) as an accurate 3D reference.
The working principle of the Rabi magnetometer is to extract the orientation of a DC magnetic field relative to the MPE from Rabi rates driven coherently on a set of hyperfine transitions by a microwave field. Importantly, we calibrate systematics such as coil system and MPE drifts, pressure shifts, and Stark shifts from an accumulation of Rabi frequencies driven at various microwave detunings. Our measurements take place in a heated microfabricated vapor cell embedded within a microwave cavity; a platform with much greater sensitivity than a previous proof-of-concept experiment with cold atoms . Depending on the direction of the DC magnetic field, we extract Rabi rates by either directly measuring Rabi oscillations or by fitting to sidebands in the Larmor free-induction-decay (FID) spectrum due to microwave dressing. Here we utilize the Faraday effect of a far-detuned probe beam to non-destructively sense atomic spin. With a full theoretical model, we understand the coherence of these Rabi oscillations to be dominated by spin-exchange collisions in a regime where current theoretical studies of hyperfine coherence that assume static atomic populations are not accurate.
 T. Thiele, Y. Lin, M. O. Brown, and C. A. Regal, Phys. Rev. Lett. 121 153202 (2018).
|Presenter name||Christopher Kiehl|