Delocalised oxygen as the origin of two-level defects in Josephson junctions

Abstract

One of the key problems facing superconducting qubits and other Josephson junction devices is the decohering effects of bi-stable material defects. Although a variety of phenomenological models exist, the true microscopic origin of these defects remains elusive. For the first time we show that these defects may arise from delocalisation of the atomic position of the oxygen in the oxide forming the Josephson junction barrier. Using a microscopic model, we compute experimentally observable parameters for phase qubits. Such defects are charge neutral but have non-zero response to both applied electric field and strain. This may explain the observed long coherence time of two-level defects in the presence of charge noise, while still coupling to the junction electric field and substrate phonons.

5 pages, 4 figures. This version streamlines presentation and focuses on the 2D model. Also fixed embarrassing typo (pF -> fF)

References in corpus (5)

• Low- and high-frequency noise from coherent two-level systems
• Magnetism in SQUIDs at Millikelvin Temperatures
• Measuring the temperature dependence of individual two-level systems by direct coherent control
• Quantitative evaluation of defect-models in superconducting phase qubits
• Microscopic model of critical current noise in Josephson-junction qubits: Subgap resonances and Andreev bound states

Cited by in corpus (3)

• Observation of directly interacting coherent two-level systems in a solid
• Microscopic models for charge-noise-induced dephasing of solid-state qubits
• Identification of structural motifs as tunneling two-level systems in amorphous alumina at low temperatures