Benchtop Magnetic Shielding for Benchmarking Atomic Magnetometers

Here, a benchtop hybrid magnetic shield containing four mumetal cylinders and nine internal flexible printed circuit boards (flex-PCBs) is designed, constructed, tested, and operated. The shield is designed specifically as a test-bed for building and operating ultrasensitive quantum magnetometers. The geometry and spacing of the mumetal cylinders are optimized to maximize shielding efficiency while maintaining Johnson noise
${ < }15$
fT/
$\sqrt {\text {Hz}}$
. Experimental measurements at the shield’s center show passive shielding efficiency of
$(1.0\pm 0.1)\times 10^{6}$
for a 0.2-Hz oscillating field applied along the shield’s axis. The nine flex-PCBs 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 to 0.23 nT.