Optical-Magnetometry-Based Current Source

We present a current monitoring system based on optical magnetometry, which is able to discriminate true current variations from environmental effects at room temperature. The system consists of a dedicated thermally stable magnetic field confining coil and an array of four optically pumped magnetometers arranged in a two-dimensional gradiometer configuration. These magnetometers are used to monitor magnetic field variations inside the coil, which are correlated to the variations of the driving current of the coil. The system uses a digital signal processing unit to extract and record in real time the magnetic field values measured by the magnetometers, which allows a real time monitoring of the current. The system's coil, which is made out of printed circuit boards, can easily be changed to adapt the current-to-field conversion; thus, we can expand the applicability of this system to a wide range of currents. By suppressing technical noise, our version of the current monitoring system shows a shot-noise limited relative sensitivity of $5 \times 10^{-8}$ on a 20 mA current at 0.5 s integration time.