Nonlinear microwave response of aluminum weak-link Josephson oscillators

TL;DR

This paper investigates the nonlinear microwave response of aluminum nanoSQUID-based resonators at millikelvin temperatures, demonstrating flux-tunable resonances, bifurcation behavior, and parametric amplification suitable for quantum computing applications.

Contribution

It provides the first detailed experimental analysis of 3D aluminum nanobridge Josephson oscillators, showing their potential for quantum bit implementation.

Findings

Flux modulation matches numerical models

Stable bifurcation observed under strong excitation

Achieved >20dB gain in parametric amplification

Abstract

We present the driven response at T=30mK of 6 GHz superconducting resonators constructed from capacitively-shunted three dimensional (3D) aluminum nanobridge superconducting quantum interference devices (nanoSQUIDs). We observe flux modulation of the resonant frequency in quantitative agreement with numerical calculation and characteristic of near-ideal short weak link junctions. Under strong microwave excitation, we observe stable bifurcation in devices with coupled quality factor (Q) ranging from ~30-3500. Near this bias point, parametric amplification with > 20dB gain, 40 MHz bandwidth, and near quantum-limited noise performance is observed. Our results indicate that 3D nanobridge junctions are attractive circuit elements to realize quantum bits.