Ultrasensitive magnetic field detection is important in a wide range of research areas and applications. Important examples are within biomagnetism, where signals from the human brain or the human (fetal) heart support medical diagnostics, and within geophysics, where the precise characterization of anomalies in the Earth magnetic field is used for mineral exploration and archeology.

The article represents a systematic study of a novel photonic quantum sensor designed for targeted applications. The main challenge of ultrasensitive sensor operation within the geomagnetic field – many orders of magnitude stronger than the faint signals of interest – was addressed using a novel readout scheme, a sensor system design enabling portable and battery driven operation, and reducing noise contributions. In extensive studies and with the unique expertise of the project partners from Thuringian industry the scientists implemented a fully integrated demonstrator and evaluated its fundamental detection limits by theoretical analysis. On top, the researchers let the novel demonstrator compete with a state-of-the-art magnetic field detector based on superconducting circuits that is already used in applications. By measurements in a shielded environment, they identified the sources of noise and determined a magnetic field resolution of 140 fT / √Hz in a signal bandwidth of up to 250 Hz which allows detecting signal amplitudes of about eight orders of magnitude lower than the surrounding Earth’s magnetic field. A final comparison of the signal quality between the established measurement system and the quantum sensor device demonstrated its performance in a real-world application. Finally, the researchers identified the tuning points for even further improvement in signal quality, bandwidth, and magnetic field resolution in a next-generation device, which is already under construction.

The work summarizes the path from the idea of a novel operational mode of atomic quantum sensors towards the demonstration of the device in real-world measurement scenarios. The article thus sketched the way from a basic of quantum technologies to application of quantum sensors in fields of environmental and life science.