High Impedance Granular Aluminum Ring Resonators

TL;DR

This paper demonstrates high-impedance superconducting ring resonators made from granular aluminum, achieving impedances over 100 kΩ with high quality factors, useful for quantum technologies and studying phase-slip physics.

Contribution

It introduces a method to create superinductors with granular aluminum achieving impedances over 100 kΩ and demonstrates their integration into ring resonators with high quality factors.

Findings

Impedances exceeding 100 kΩ in the 4-8 GHz range.

Quality factors around 10^5 in the single-photon regime.

Observed low non-linearity and frequency noise spectral densities of 10^2 to 10^3 Hz/√Hz.

Abstract

Superconducting inductors with impedance surpassing the resistance quantum, i.e., superinductors, are important for quantum technologies because they enable the development of protected qubits, enhance coupling to systems with small electric dipole moments, and facilitate the study of phase-slip physics. We demonstrate superinductors with densely packed meandered traces of granular aluminum (grAl) with inductances up to $4\,\mu\mathrm{H}$, achieving impedances exceeding $100\,\mathrm{k}\Omega$ in the $4-8\,\mathrm{GHz}$ range. Ring resonators made with grAl meandered superinductors exhibit quality factors on the order of $10^5$ in the single-photon regime and low non-linearity on the order of tens of $\mathrm{Hz}$. Depending on the grAl resistivity, at $10\,\mathrm{Hz}$, we measure frequency noise spectral densities in the range of $10^2$ to $10^3\,\mathrm{Hz}/\sqrt{\mathrm{Hz}}$. In some devices, in the single-photon regime, we observe a positive Kerr coefficient of unknown origin. Using more complex fabrication, the devices could be released from the substrate, either freestanding or suspended on a membrane, thereby further improving their impedance by a factor of three.