The effects of disorder in superconducting materials on qubit coherence

TL;DR

This study systematically investigates how material disorderness in superconducting superinductors affects qubit coherence, revealing that flux noise correlates with disorderness, providing insights for material optimization.

Contribution

It offers a detailed correlation between material disorderness and flux noise in fluxonium qubits, advancing understanding of decoherence mechanisms in superconducting qubits.

Findings

Flux noise dominates decoherence near flux-frustration points.

Dielectric loss remains low across various material properties.

A phenomenological relation between spin defect density and disorderness was established.

Abstract

Introducing disorderness in the superconducting materials has been considered promising to enhance the electromagnetic impedance and realize noise-resilient superconducting qubits. Despite a number of pioneering implementations, the understanding of the correlation between the material disorderness and the qubit coherence is still developing. Here, we demonstrate a systematic characterization of fluxonium qubits with the superinductors made from titanium-aluminum-nitride with varied disorderness. From qubit noise spectroscopy, the flux noise and the dielectric loss are extracted as a measure of the coherence properties. Our results reveal that the $1/f$ flux noise dominates the qubit decoherence around the flux-frustration point, strongly correlated with the material disorderness; while the dielectric loss remains low under a wide range of material properties. From the flux-noise amplitudes, the areal density ($\sigma$) of the phenomenological spin defects and material disorderness are found to be approximately correlated by $\sigma \propto \rho_{xx}^3$, or effectively $(k_F l)^{-3}$. This work has provided new insights on the origin of decoherence channels within superconductors, and could serve as a useful guideline for material design and optimization.