Precise Measurement of Magnetic Field Gradients from Free Spin Precession Signals of $^{3}$He and $^{129}$Xe Magnetometers

TL;DR

This paper presents a highly precise method for measuring magnetic field gradients using free precession signals of polarized $^3$He and $^{129}$Xe gases, achieving sub-pT/cm accuracy with long relaxation times and SQUID detection.

Contribution

It introduces a novel approach combining long relaxation times and SQUID sensors to measure magnetic field gradients with unprecedented precision.

Findings

Residual longitudinal field gradient measured as (5.6 ± 0.4) pT/cm

Achieved magnetic gradient measurement accuracy below 1 pT/cm

Demonstrated stable measurements over 100 hours

Abstract

We report on precise measurements of magnetic field gradients extracted from transverse relaxation rates of precessing spin samples. The experimental approach is based on the free precession of gaseous, nuclear spin polarized $^3$He and $^{129}$Xe atoms in a spherical cell inside a magnetic guiding field of about 400 nT using LT$_C$ SQUIDs as low-noise magnetic flux detectors. The transverse relaxation rates of both spin species are simultaneously monitored as magnetic field gradients are varied. For transverse relaxation times reaching 100 h, the residual longitudinal field gradient across the spin sample could be deduced to be$|\vec{\nabla}B_z|=(5.6 \pm 0.4)$ pT/cm. The method takes advantage of the high signal-to-noise ratio with which the decaying spin precession signal can be monitored that finally leads to the exceptional accuracy to determine magnetic field gradients at the sub pT/cm scale.