Atomic delocalisation as a microscopic origin of two-level defects in Josephson junctions

TL;DR

This paper proposes a microscopic model linking atomic delocalisation of oxygen in Josephson junction oxides to two-level defects, shedding light on decoherence sources in quantum circuits.

Contribution

It introduces a novel atomic-level model for two-level defects based on oxygen delocalisation, advancing understanding of decoherence in Josephson junctions.

Findings

Atomic delocalisation can produce two-level defect behavior.

The model predicts defect responses to electric fields and strain.

Results align with experimental observations of decoherence sources.

Abstract

Identifying the microscopic origins of decoherence sources prevalent in Josephson junction based circuits is central to their use as functional quantum devices. Focussing on so called "strongly coupled" two-level defects, we construct a theoretical model using the atomic position of the oxygen which is spatially delocalised in the oxide forming the Josephson junction barrier. Using this model, we investigate which atomic configurations give rise to two-level behaviour of the type seen in experiments. We compute experimentally observable parameters for phase qubits and examine defect response under the effects of applied electric field and strain.