Ultra-Highly Linear Magnetic Flux-to-Voltage response in Proximity-based Mesoscopic bi-SQUIDs

TL;DR

This paper introduces a new proximity-based mesoscopic bi-SQUID design using aluminum and copper, demonstrating highly linear magnetic flux-to-voltage response suitable for quantum sensing and RF signal processing.

Contribution

It presents an alternative fabrication of bi-SQUIDs with tunable characteristics via metallic weak-link geometry, achieving high linearity comparable to traditional tunnel junction devices.

Findings

Linearity up to 45 dB in flux-to-voltage response.

Effective operation from 30 mK to 1 K.

Comparable performance to conventional tunnel junction bi-SQUID arrays.

Abstract

Superconducting double-loop interferometers (bi-SQUIDs) have been introduced to produce magnetic flux sensors specifically designed to exhibit ultra-highly linear voltage response as a function of the magnetic flux. These devices are very important for the quantum sensing and for signal processing of signals oscillating at the radio-frequencies range of the electromagnetic spectrum. Here, we report an Al double-loop bi-SQUIDs based on proximitized mesoscopic Cu Josephson junctions. Such a scheme provides an alternative fabrication approach to conventional tunnel junction-based interferometers, where the junction characteristics and, consequently, the magnetic flux-to-voltage and magnetic flux-to-critical current device response can be largely and easily tailored by the geometry of the metallic weak-links. We discuss the performance of such sensors by showing a full characterization of the device switching current and voltage drop \textit{vs.} magnetic flux for temperatures of operation ranging from 30 mK to $\sim 1$ K. The figure of merit of the transfer function and of the total harmonic distortion are also discussed. The latter provides an estimate of the linearity of the flux-to-voltage device response, which obtained values as large as 45 dB. Such a result let us foresee a performance already on pair with that achieved in conventional tunnel junction-based bi-SQUIDs arrays composed of hundreds of interferometers.