Structural control of two-level defect density revealed by high-throughput correlative measurements of Josephson junctions

TL;DR

This study uses high-throughput, correlated measurements to understand and control the microstructural origins of two-level system defects in Josephson junctions, leading to reduced defect density.

Contribution

It introduces a data-driven, high-throughput methodology linking fabrication microstructure to TLS occurrence in Josephson junctions, enabling defect mitigation.

Findings

Strong correlation between Al electrode microstructure and TLS density.

Two-thirds reduction in TLS achieved by changing fabrication parameters.

Large dataset of 6,000 JJs and 600 TEM images used for analysis.

Abstract

Materials defects in Josephson junctions (JJs), often referred to as two-level systems (TLS), couple to superconducting qubits and are a critical bottleneck for scalable quantum processors. Despite their importance, understanding the microscopic sources of TLS and how to mitigate them has remained a major challenge. Here, we demonstrate a high-throughput, correlated approach to trace the microstructural origins of strongly-coupled TLS in Josephson circuits. We assembled a massive dataset of TLS across 6,000 Al/AlOx/Al JJs and more than 600 atomic resolution transmission electron microscopy images. We statistically link fabrication, microstructure, and TLS occurrence, revealing a strong correlation between Al electrode thickness, Al grain size, and TLS density. Correspondingly, we find a two-thirds reduction in TLS prompted by a change in electrode fabrication parameters. These results demonstrate a robust, data-driven methodology to understand and control defects in quantum circuits and pave the way for significantly reducing TLS density.