Multi-terminal multi-junction dc SQUID for nanoscale magnetometry

TL;DR

This paper proposes a multi-terminal, multi-junction SQUID design that enables continuous adjustment of the interference pattern, allowing for sensitive magnetometry across all magnetic field values, overcoming limitations of traditional nanoSQUIDs.

Contribution

It introduces a theoretical model for multi-terminal, multi-junction SQUIDs that can be tuned with control currents to maintain maximum sensitivity at any magnetic field value.

Findings

Operation at maximum sensitivity is achievable at any magnetic field value.

The model describes how control currents shift the interference pattern.

The approach allows direct measurement of superconducting junction current-phase relations.

Abstract

Miniaturization of superconducting quantum interference devices (SQUIDs) is of major importance for the development of sensitive scanning nanoscale magnetometry tools. The high sensitivity of nanoSQUIDs is restricted, however, to only particular periodic values of the applied magnetic field, making accurate measurements at intermediate values of the field impossible. We present a theoretical investigation of a multi-terminal, multi-junction SQUID (mSQUID) that lifts this limitation by providing electrical means for a continuous shift of the quantum interference pattern with respect to the applied field. Analysis of 4-terminal, 4-junction and 3-terminal, 3-junction mSQUIDs shows that operation at maximum sensitivity can be obtained at any value of the magnetic field by applying control current to the extra terminals. The model describes the variation and the shift of the interference pattern as a function of the control currents, junction asymmetries, and the mSQUID inductance. The mSQUID is also shown to provide a direct measurement of the current-phase relations of superconducting junctions. The derived model provides a quantitative description of the recently developed multi-terminal nanoSQUID-on-tip.