Toward a Laser‐Free Diamond Magnetometer for Microwave Fields

Abstract The nitrogen‐vacancy (NV) center in diamond is a unique magnetometer. Its atomic size enables integrations of a tremendous amount ( n NV ) of NV centers in a bulk diamond with a sensitivity scaling as . However, such a bulk sensor requires a high‐power laser to polarize and read out the NV centers. The increasing thermal damage and additional noises associated with high‐power lasers hinder the growth of n NV , and thus limit the sensitivity at picotesla level. Here, it shows a relaxometry‐based microwave magnetometer that the power density is determined by the relaxation time T 1 . By cooling the diamond sensor to prolong the T 1 (≈s), the required power density further reduces to , of the saturation value. This work paves the way for the utilization of large‐size diamond to promote the sensitivity of diamond magnetometer to femtotesla level and beyond.