Benchtop magnetic shielding for benchmarking atomic magnetometers

TL;DR

This paper presents the design, construction, and testing of a benchtop magnetic shield optimized for benchmarking ultra-sensitive atomic magnetometers, achieving high shielding efficiency and precise field control.

Contribution

It introduces a novel hybrid magnetic shield with optimized geometry and integrated field generation, tailored for quantum magnetometer testing and calibration.

Findings

Passive shielding efficiency of ~10^6 at 0.2 Hz

Active null reduces static field from 1.68 nT to 0.23 nT

Field uniformity deviations within 0.5% over target regions

Abstract

Here, a benchtop hybrid magnetic shield containing four mumetal cylinders and nine internal flexible printed circuit boards is designed, constructed, tested, and operated. The shield is designed specifically as a test-bed for building and operating ultra-sensitive quantum magnetometers. The geometry and spacing of the mumetal cylinders are optimized to maximize shielding efficiency while maintaining Johnson noise $<15$ fT/$\sqrt{}$Hz. Experimental measurements at the shield's center show passive shielding efficiency of $\left(1.0\pm0.1\right){\times}10^6$ for a $0.2$ Hz oscillating field applied along the shield's axis. The nine flexible printed circuit boards generate three uniform fields, which all deviate from perfect uniformity by ${\leq}0.5$% along $50$% of the inner shield axis, and five linear field gradients and one second-order gradient, which all deviate by ${\leq}4$% from perfect linearity and curvature, respectively, over measured target regions. Together, the target field amplitudes are adjusted to minimize the remnant static field along $40$% of the inner shield axis, as mapped using an atomic magnetometer. In this region, the active null reduces the norm of the magnitudes of the three uniform fields and six gradients by factors of $19.5$ and $19.8$, respectively, thereby reducing the total static field from $1.68$ nT to $0.23$ nT.