A stable, single-chip, two-dimensional gradiometric device based on two superconducting quantum interference devices

The fabrication of two-dimensional gradiometric devices consisting of two superconducting quantum interference devices (SQUIDs) and pickup coils made from a low-critical temperature superconductor was discussed. A square superconducting shield was used to cover the the region of overlap between the two orthogonal SQUIDs around the center of the substrate to minimize the cross-talk between the SQUIDs. Cross-talk ratio was measured by operating both gradiometers in the flux-locked loops (FLL) and the magnetic flux through each was measured when a sinusoidal magnetic flux was applied to one of the feedback coils. It was found that the noise of the SQUID devices was more stable under a changing field due to its parallel structure.