The influence of pinholes and weak-points in aluminium-oxide Josephson junctions

Abstract

Josephson junctions are the key components used in superconducting qubits for quantum computing. The advancement of quantum computing is limited by a lack of stability and reproducibility of qubits which ultimately originates in the amorphous tunnel barrier of the Josephson junctions and other material imperfections. Pinholes in the junction have been suggested as one of the possible contributors to these instabilities, but evidence of their existence and the effect they might have on transport is unclear. We use molecular dynamics to create three-dimensional atomistic models to describe Al-AlOx-Al tunnel junctions, showing that pinholes form when oxidation of the barrier is incomplete. Following this we use the atomistic model and simulate the electronic transport properties for tunnel junctions with different barrier thicknesses using the non-equilibrium Green's function formalism. We observe that pinholes may contribute to excess quasiparticle current flow in Al-AlOx-Al tunnel junctions with thinner barriers, and in thicker barriers we observe weak-points which facilitate leakage currents even when the oxide is continuous. We find that the disordered nature of the amorphous barrier results in significant variations in the transport properties. Additionally, we determine the current-phase relationship for our atomistic structures, confirming that devices with pinholes and weak-points cause a deviation from the ideal sinusoidal Josephson relationship.

17 pages, 15 figures

References in corpus (9)

• Exponential suppression of bit or phase flip errors with repetitive error correction
• Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
• Observation of Josephson Harmonics in Tunnel Junctions
• Merged-Element Transmons: Design and Qubit Performance
• Are pinholes the cause of excess current in superconducting tunnel junctions? A study of Andreev current in highly resistive junctions
• Path toward manufacturable superconducting qubits with relaxation times exceeding 0.1 ms
• Microscopic Model of Critical Current Noise in Josephson Junctions
• Quantitative evaluation of defect-models in superconducting phase qubits
• Probing defect densities at the edges and inside Josephson junctions of superconducting qubits

Cited by in corpus (2)

• Analysis of Josephson Junction Barrier Variation: A Combined Electron Microscopy, Breakdown and Monte-Carlo Approach
• Towards a $\cos (2\phi )$ Josephson element using aluminum junctions with well-transmitted channels