Optimised hybrid shielding and magnetic field control for emerging quantum technologies
2021
The accurate control of magnetic fields is a cornerstone of multiple emerging quantum technologies. These
technologies often require passive high permeability magnetic shielding and internal active field-generating coils
to create their own bespoke magnetic field landscape. However, magnetic fields generated by coils are distorted
by high permeability shielding, preventing the accurate and efficient generation of the desired field environment.
Here, we design a cylindrical four-layer magnetic shield with an interior hybrid active-passive coil system that is
explicitly optimised to include the electromagnetic coupling between the active and passive components. We use
a combination of analytical methods and numerical simulations to determine the shield parameters - geometry,
thickness, and access hole positions - to maximise the passive shielding efficiency and minimise the shield-induced
Johnson noise and weight. Then, we apply an analytical formulation of the magnetic field, which accounts for
the interaction with the magnetic shield, to design nine orthogonal hybrid active-passive field-generating coils
inside the shield. The coils will be manufactured on thin low-via flex-PCBs near the shield's interior surface
and generate three uniform fields and six gradient fields that deviate by less than 0.4% and 2%, respectively,
over an internal cylindrical region extending over half the diameter and length of the innermost shield layer.
These hybrid active-passive coils can accurately remove deviations in the background field or generate various
complex magnetic field landscapes. Consequently, the hybrid shield provides an ideal platform for miniaturising
and commercialising quantum technologies that require precisely-controlled magnetic fields within a low-noise
environment.
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