Sub-picotesla widely tunable atomic magnetometer operating at room-temperature in unshielded environments

We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded environments and near room temperature with a measured sensitivity of 130 fT/$Hz$⁠. We demonstrate consistent, narrow-bandwidth operation across the kHz–MHz band, corresponding to three orders of magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback loop actively and automatically stabilizes the magnetic field around the sensor. We measure a reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm³, increases the spatial resolution of the measurements. Low temperature operation, without any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically extends the range of potential field applications for our device.