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 (17)

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Cited by in corpus (18)

• Towards understanding two-level-systems in amorphous solids -- Insights from quantum circuits
• Observation of directly interacting coherent two-level systems in a solid
• Low-frequency charge noise in Si/SiGe quantum dots
• Projected dipole moments of individual two-level defects extracted using circuit quantum electrodynamics
• Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits
• 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
• Quantum-limited measurement of spin qubits via curvature coupling to a cavity
• The effect of atomic structure on the electrical response of aluminium oxide tunnel junctions
• Non-equilibrium probing of two-level charge fluctuators using the step response of a single electron transistor
• Probing hundreds of individual quantum defects in polycrystalline and amorphous alumina
• Structural and Nanochemical Properties of AlOx Layers in $Al/Al{O}_x/Al$-Layer Systems for Josephson Junctions
• Constructing ab initio models of ultra-thin Al-AlOx-Al barriers
• Atomic delocalisation as a microscopic origin of two-level defects in Josephson junctions
• Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes
• Experimentally revealing anomalously large dipoles in a quantum-circuit dielectric
• Anomalous low-energy properties in amorphous solids and the interplay of electric and elastic interactions of tunneling two-level systems
• A 3D investigation of delocalised oxygen two-level defects in Josephson junctions