Approaching ideal weak link behavior with three dimensional aluminum nanobridges

TL;DR

This study demonstrates that three-dimensional aluminum nanobridges in SQUIDs can nearly reach ideal weak link behavior, significantly improving magnetic flux modulation and potential applications in sensitive magnetometers and quantum devices.

Contribution

The paper introduces 3D aluminum nanobridges as superior weak links in SQUIDs, achieving near-ideal critical current modulation compared to traditional 2D structures.

Findings

3D nanobridge SQUIDs show ~70% critical current modulation

L ≤ 150 nm nanobridges approach ideal weak link behavior

Enhanced nonlinearity benefits quantum sensing and low-noise applications

Abstract

We present transport measurements of unshunted dc superconducting quantum interference devices (SQUIDs) consisting of 30 nm wide aluminum nanobridges of varying length L contacted with two and three dimensional banks. 3D nanobridge SQUIDs with L $\leq$ 150 nm (approximately 3-4 times the superconducting coherence length) exhibit $\approx 70%$ critical current modulation with applied magnetic field, approaching the theoretical limit for an ideal short metallic weak link. In contrast, 2D nanobridge SQUIDs exhibit significantly lower critical current modulation. This enhanced nonlinearity makes 3D nanobridge Josephson junctions well suited to optimize sensitivity in weak link SQUID magnetometers as well as realize ultra low-noise amplifiers and qubits.