A 3D investigation of delocalised oxygen two-level defects in Josephson junctions

TL;DR

This study extends the delocalized oxygen model of two-level defects in Josephson junctions from 2+1D to full 3D, providing deeper insights into defect origins and their impact on quantum device decoherence.

Contribution

The paper develops a comprehensive 3D quantum model of delocalized oxygen defects in Josephson junctions, enhancing understanding of their microscopic nature and effects.

Findings

3D model aligns with experimental parameters for phase qubits

Delocalized oxygen atoms are characterized within strained and amorphous lattices

The approach improves defect identification and mitigation strategies

Abstract

Environmental two-level systems (TLS) have been identified as significant decoherence sources in Josephson junction (JJ) based circuits. For such quantum devices to be functional, the removal or control of the TLS is a necessity. Understanding the microscopic origins of the 'strongly coupled' TLS type is one current path of investigation to that end. The delocalized oxygen model suggests the atomic position of an oxygen atom is spatially delocalized in the oxide forming the JJ barrier. In this report we extend this model from its previous 2+1D construction to a complete 3D description using a Wick-rotated time-dependent Schrodinger equation to solve for time-independent solutions in three dimensions. We compute experimentally observable parameters for phase qubits and compare the results to the 2+1D framework. We devise a Voronoi classification scheme to investigate oxygen atoms delocalizing within strained and non-strained crystalline lattices, as well as realistic atomic positions a JJ amorphous tunnel barrier constructed in previous density functional studies.