Approaching ideal weak link behavior with three dimensional aluminum nanobridges

We investigate unshunted dc superconducting quantum interference devices (SQUIDs) consisting of aluminum nanobridges of varying length L contacted with (two dimensional, or 2D) and (three dimensional, or 3D) banks. 3D nanobridge SQUIDs with L≤150 nm (approximately four times the superconducting coherence length) exhibit ≈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 ultralow-noise amplifiers and qubits.