Toward T2-Limited DC Diamond Quantum Magnetometry via Flux Concentration and Modulation

High-sensitivity magnetometry is of critical importance to the fields of biomagnetism and geomagnetism. However, magnetometry for dc and low-frequency signal detection faces the challenge of sensitivity improvement, resulting from the low-frequency noise induced by multiple types of noise sources. In particular, for the solid-state spin dc quantum magnetometry, the sensitivity has been limited by short dephasing time. Here, we realized the conversion of the magnetic signal from dc to ac by utilizing a flux concentration and modulation (FCM) technique so that the dynamical decoupling method can be applied to prolong the dephasing time. Hence, we have successfully demonstrated a dc magnetometer with a sensitivity of 32 pT/Hz
$^{{1}/{2}}$
, which is about two orders of magnitude over that of the Ramsey-type dc magnetometer. Further enhancement of the sensitivity is systematically analyzed, although is challenging but plenty of room is achievable. Our results shed light on the realization of room temperature dc quantum magnetometry with femtotesla-sensitivity in the future.