Circuit Quantum Electrodynamics of Granular Aluminum Resonators

TL;DR

This paper investigates the quantum electrodynamics properties of granular aluminum microwave resonators, revealing their nonlinear behavior and high quality factors, which are promising for quantum computing and sensing applications.

Contribution

It provides the first comprehensive measurement and modeling of GrAl resonators' quantum electrodynamics properties across a wide frequency range, highlighting their nonlinearity and potential uses.

Findings

Self-Kerr coefficients from 10^{-2} Hz to 10^5 Hz.

High quality factors around 10^5.

Agreement between experimental results and analytic models.

Abstract

The introduction of crystalline defects or dopants can give rise to so-called "dirty superconductors", characterized by reduced coherence length and quasiparticle mean free path. In particular, granular superconductors such as Granular Aluminum (GrAl), consisting of remarkably uniform grains connected by Josephson contacts have attracted interest since the sixties thanks to their rich phase diagram and practical advantages, like increased critical temperature, critical field, and kinetic inductance. Here we report the measurement and modeling of circuit quantum electrodynamics properties of GrAl microwave resonators in a wide frequency range, up to the spectral superconducting gap. Interestingly, we observe self-Kerr coefficients ranging from $10^{-2}$ Hz to $10^5$ Hz, within an order of magnitude from analytic calculations based on GrAl microstructure. This amenable nonlinearity, combined with the relatively high quality factors in the $10^5$ range, open new avenues for applications in quantum information processing and kinetic inductance detectors.