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Physical Review A

Three-axis isotropic-sensitivity He4 magnetometer with alignment-based longitudinal parametric resonance

Bowen Wang, Xiang Peng, Wei Xiao, Hong Mei Guo

Published Dec 12, 2022• 6 citations
Publisher

Abstract

For measurements in near-zero magnetic fields, vector atomic magnetometers are promising alternatives to scalar versions, but generally suffer from inconsistent performance over three axes. We present a single-beam vector magnetometer with three-axis isotropic sensitivity based on $^{4}\mathrm{He}$ atomic alignment. Longitudinal parametric resonance with atoms pumped by linearly polarized light is proposed for the $z$-axis measurement, while the Hanle effect in transverse geometry is used for $x$- and $y$-axis measurements. The evolution of atomic alignment multipole components and expressions of the three-axis magnetic responses are analyzed in detail. We describe the experimental operation of the proposed magnetometer with a magnetic-field noise floor of $150\phantom{\rule{0.16em}{0ex}}\mathrm{fT}/{\mathrm{Hz}}^{1/2}$ for the three axes, which is attractive for biomagnetism requiring vector characterization and source reconstruction.

DOI
10.1103/physreva.106.063102

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For measurements in near-zero magnetic fields, vector atomic magnetometers are promising alternatives to scalar versions, but generally suffer from inconsistent performance over three axes. We present a single-beam vector magnetometer with three-axis isotropic sensitivity based on 4He^{4}\mathrm{He}4He atomic alignment. Longitudinal parametric resonance with atoms pumped by linearly polarized light is proposed for the zzz-axis measurement, while the Hanle effect in transverse geometry is used for xxx- and yyy-axis measurements. The evolution of atomic alignment multipole components and expressions of the three-axis magnetic responses are analyzed in detail. We describe the experimental operation of the proposed magnetometer with a magnetic-field noise floor of 150fT/Hz1/2150\phantom{\rule{0.16em}{0ex}}\mathrm{fT}/{\mathrm{Hz}}^{1/2}150fT/Hz1/2 for the three axes, which is attractive for biomagnetism requiring vector characterization and source reconstruction.
Three-axis atomic magnetometers have great advantages for interpreting information conveyed by magnetic fields. Here, we demonstrate a compact construction of a three-axis vector atomic magnetometer. The magnetometer is operated with a single laser beam and with a specially designed triangular 87Rb vapor cell (side length is 5 mm). The ability of three-axis measurement is realized by reflecting the light beam in the cell chamber under high pressure, so that the atoms before and after reflection are polarized along two different directions. It achieves a sensitivity of 40 fT/Hz in x-axis, 20 fT/Hz in y-axis, and 30 fT/Hz in z-axis under spin-exchange relaxation-free regime. The crosstalk effect between different axes is proven to be little in this configuration. The sensor configuration here is expected to form further values, especially for vector biomagnetism measurement, clinical diagnosis, and field source reconstruction.
In parametric-resonance magnetometers (PRMs), optically pumped atoms subject to rf fields allow one to measure the components of a very low magnetic field. Here, instead of using a circularly polarized light for creating atomic orientation, as in previous works, a linearly polarized light is used for creating atomic alignment. A dressed-atom formalism introduced by Polonsky and Cohen-Tannoudji is extended and allows one to map this situation to a simpler Hanle effect on aligned atoms. Analytical expressions for all alignment tensor components and photodetection signals are obtained for both the Hanle magnetometer and PRMs. A two-rf field alignment PRM is shown to display several improvements from its orientation counterpart, providing a secular third axis sensitivity and a lower degradation from the one-axis sensitivity obtained by using a single rf field. These specificities are shown to result from the apparent depolarization of the pumping light acting on the atom dressed by two-rf fields. Experimental measurements showing a good agreement with the theoretical predictions are presented.
Parametric-resonance magnetometer is a high-sensitivity quantum sensor characterized by applying the non-resonant radio-frequency (RF) fields to the atomic ensemble. The RF fields lead to crosstalk in the multi-sensor design, thus disturbing the magnetic-field measurement results. We propose an optically modulated alignment-based 4He parametric-resonance magnetometer. By using the fictitious field generated by the modulated light shift, parametric resonance is realized, and crosstalk caused by the magnetic RF field is prevented. The relative intensity noise of the lasers is suppressed to optimize the sensitivity of the magnetometer. Our magnetometer experimentally demonstrates a magnetic-field noise floor of 130 fT/Hz1/2 in both open- and closed-loop operations and has the potential to reach 70 fT/Hz1/2 when compared with the optimized magnetic RF scheme. It provides near-zero magnetic-field measurements with a 2 kHz bandwidth at room temperature, which is useful for high-bandwidth measurements in biomagnetic applications.
We demonstrate a single-beam atomic magnetometer (AM) capable of measuring a three-axis magnetic field with high-sensitivity, achieved by applying a small DC offset field and a high frequency modulation field. To satisfy the miniaturization demand of AMs, an elliptically polarized light detuned by 50 GHz from the resonance transition center is employed. The circularly polarized component is used to polarize the alkali-metal atoms, while the linearly polarized light is used to detect the dynamics of the polarized spin under a magnetic field. Based on theoretical analysis, parameters that significantly affect the performance are optimized, and a sensitivity of 20 fT/Hz 1/2 in x -axis, 25 fT/Hz 1/2 in y -axis, 30 fT/Hz 1/2 in z -axis is achieved with a miniature 4 × 4 × 4 mm 87 Rb vapor cell. Moreover, we also verify that the operation principle of AMs can be used to null background magnetic fields in-situ with isotropic compensation resolution of 6.7 pT, which provides an effectively precise method for zeroing ambient magnetic field. The high-sensitivity operating of an elliptically-polarized-laser-based magnetometer provides prospective futures for constructing a compact, low-cost AM, which is particularly applicable for non-invasive bio-magnetic imaging such as array-based magnetoencephalography (MEG) and magnetocardiography (MCG).
Abstract In this paper, we demonstrate a three-axis atomic magnetometer based on parametric oscillations, which can measure the three magnetic field components simultaneously and independently. A circularly polarized pump beam is applied to create the spin polarization, and another linearly polarized probe beam is used to detect the dynamics of the polarized spin under a magnetic field. With a closed-loop system to keep the magnetic field in resonance with the atoms, three components of magnetic field are measured by their feedback signals. We achieve a magnetometer sensitivity of 6 pT ( ) −1 , 25 pT ( ) −1 , and 60 pT ( ) −1 along three axes in the frequency range from 100 Hz to 1 kHz with a bandwidth better than 1 kHz under an unshielded environment. Furthermore, this magnetometer is free of optical modulation, which reduces the complexity of experimental setups. The methods we present here provide a prototype all-electrical three-axis atomic magnetometer.
A three-axis atomic magnetometer employing longitudinal field modulation is demonstrated theoretically and experimentally. The operational condition of this magnetometer is that the longitudinal z-component of the external magnetic field is dominant, which is achieved by applying a bias magnetic field. The longitudinal z-component of the external magnetic field is extracted from the modulation frequency, which tracks the resonance frequency, and the transversex- andy- components are, respectively, obtained from the quadrature and the in-phase signals of a lock-in amplifier. Through feedback control, the magnitude and direction of an external magnetic field can be measured in real time, and an excellent orthogonality of the three-axis magnetometer response is obtained. By optimizing the parameters of this three-axis magnetometer, a longitudinal field sensitivity of 0.3pT/Hz1/2{\rm{pT}/ \rm{Hz}}^{1/ 2}pT/Hz1/2and a transverse field sensitivity of 2pT/Hz1/2{\rm{pT}/ \rm{Hz}}^{1/ 2}pT/Hz1/2are achieved.