Magnetometry with spin polarized Hydrogen from molecular photo-dissociation

Abstract

In a recent publication [arXiv:2010.14579], we introduced a new type of atomic magnetometer, which relies on hydrohalide photo-dissociation to create high-density spin-polarized hydrogen. Here, we extend our previous work and present a detailed theoretical analysis of the magnetometer signal and its dependence on time. We also derive the sensitivity for a spin-projection noise limited magnetometer, which can be applied to an arbitrary magnetic field waveform.A broad range of physical objects and processes generate magnetic fields which upon detection can convey important information about the nature and structure of their origin. As a result, magnetic field detection lies at the heart of many scientific and technological applications, which can benefit significantly from advances in magnetometry [1].Different magnetic field sensors have been developed which offer distinct advantages and are attractive for particular applications. In general terms, an ideal magnetometer should present high-sensitivity, wide bandwidth detection, highperformance over a large dynamic range and operating conditions, as well as capability for miniaturization when used for magnetic field imaging.Recently, a new type of atomic magnetometer was demonstrated based on high-density spin-polarized atomic H (SPH) [2], which has the potential to address satisfactorily the above requirements for magnetometry. The spinpolarized ensemble is produced by photo-dissociating hydrohalide gas with a circularly-polarized laser pulse [3][4][5]. Magnetic field detection is achieved by monitoring the dynamics of the H hyperfine coherences, which are created in the optical pumping process without the need for external magnetic fields.This paper is an extension of the work presented in [2], analytically deriving equations for the spin-dynamics, the magnetometer signal and the quantum spin-projection noise.We will consider the magnetometer scheme with mutually orthogonal directions for optical pumping, magnetic field direction and spin-probing, as shown in Fig. 1. Without loss of generality we take the magnetic field to be in the z direction, the optical pumping along the y axis and the probe axis in the x direction. Monitoring of spins is realized with an inductive pick-up coil, which detects the magnetic flux generated by the H spins. Since the electron magnetic moment is more than three orders of magnitude larger than the proton magnetic moment, the coil is to a very good approximation only sensitive to the H electron spins. In the following, we will assume a pickup coil with a response time much shorter than the hyperfine interaction period and neglect complications arising from a non-spherical polarized region or from geometrical factors in the coupling of the magnetic field from spins to the coil. For simplicity, we will assume that the observable is d Ŝx dt , where Ŝi expresses the dimensionless electron spin operator in the i direction.