Optically pumped quantum magnetometer with combined advantages of $M_X$ and $M_Z$ devices

A scheme of the magnetometer that simultaneously employs $M_X$ and $M_R$ magnetic resonance signals with the latter signal related to the radial component of the rotating atomic magnetic moment is proposed and tested. With respect to the shape, dynamic characteristics, and metrological parameters, the $M_R$ signal is similar to the $M_X$ signal that is widely used in magnetometry but the former signal can be detected simultaneously with the $M_X$ signal using a common radio optical scheme. The proposed device represents a fast $M_X$ magnetometer with the phase in the feedback loop that is controlled by a slow precise $M_R$ magnetometer implemented using the same atoms. The device that can be based on a conventional $M_X$ sensor simultaneously exhibits a relatively short response time ($\tau\le$ 0.1 s) and the accuracy that is approximately equal to the resolution of the quantum $M_X$ discriminator at times of 10–100 s. The scheme is experimentally tested, and the statistic estimate of reproducibility is (1.2 $\pm$ 1.1) pT.