Femtotesla Nearly-Quantum-Noise-Limited Pulsed Gradiometer at Earth-Scale Fields

Applications of optical magnetometers in demanding environments require a high common-mode rejection ratio (CMRR) to effectively suppress ambient noise, but challenges still remain to achieve experimental sensitivity at the quantum noise level. The authors develop a compact magnetic gradiometer featuring a high CMRR and a differential sensitivity of tens of femtoteslas over a broad dynamic range, including Earth's field magnitude. This gradiometer is also nearly quantum-noise-limited, which is compatible with quantum enhancement techniques in geomagnetic fields and can be used in unshielded environments such as space science, navigation, and biomedicine.