Analysis of Josephson Junction Barrier Variation: A Combined Electron Microscopy, Breakdown and Monte-Carlo Approach

TL;DR

This paper combines electron microscopy, breakdown testing, and Monte-Carlo simulations to analyze and optimize the barriers in Josephson junctions, crucial for superconducting quantum computing.

Contribution

It introduces an integrated approach using microscopy, electrical breakdown, and simulations to better understand and improve Josephson junction barriers.

Findings

Monte-Carlo simulations show 15-20% thickness variation is compatible with data.

Breakdown voltage grouping reveals sub-ensembles with different resistances.

Electron microscopy faces challenges in accurately determining barrier thickness distribution.

Abstract

Josephson junctions manufactured to tight tolerances are necessary components for superconducting quantum computing. Developing precise manufacturing techniques for Josephson junctions requires an understanding of their make-up and robust feedback metrics against which to optimise. Here we consider complementary techniques assessing what conclusions they allow us to draw about the barriers in junctions. Monte-Carlo simulations of barriers show that standard deviations of 15-20% of the total barrier thickness are compatible with our experimental data. Electrical breakdown allows us to probe the weakest points in barriers. Narrowing the distribution of this breakdown provides a promising feedback mechanism for barrier optimisation. Grouping junctions by breakdown voltage allows us to identify sub-ensembles of junctions with different median resistance. Transmission electron microscopy can be used to find average barrier thickness, although we highlight challenges forming robust conclusions on the distribution of thicknesses in a barrier from these experiments.