High-Sensitivity rf Detection Using an Optically Pumped Comagnetometer Based on Natural-Abundance Rubidium with Active Ambient-Field Cancellation

This is the authors' abstract. We don't add key points for this paper.

To detect a specific radio-frequency (rf) magnetic field, rf optically pumped magnetometers (OPMs) require a static magnetic field to set the Larmor frequency of the atoms equal to the frequency of interest. However, unshielded and variable magnetic field environments (e.g., an rf OPM on a moving platform) pose a problem for rf OPM operation. Here, we demonstrate the use of a natural-abundance rubidium vapor to make a comagnetometer to address this challenge. Our implementation builds upon the simultaneous application of several OPM techniques within the same vapor cell. First, we use a modified implementation of an OPM variometer based on ⁸⁷Rb$ to detect and actively cancel unwanted external fields at frequencies $⪅60{{0.2em}{0ex}}Hz$ using active feedback to a set of field control coils. We exploit this stabilized field environment to implement a high-sensitivity rf magnetometer using ${}⁸⁵Rb. Using this approach, we demonstrate the ability to measure rf fields with a sensitivity of approximately 90.2em0exfT0.1em0exHz^-1/2 inside a magnetic shield in the presence of an applied field of approximately 200.2em0exμT along three mutually orthogonal directions. This demonstration opens up a path toward completely unshielded operation of a high-sensitivity rf OPM.