Karen Bayros, RMIT
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 is likely to originate in the disordered oxide tunnel barrier in the Josephson junctions that constitute the qubits. Pinholes have been suggested as one of the possible contributors to these instabilities, but evidence of their existence and the effects 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 small amounts of oxide are grown in the barrier. 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 single-electron current flow in Al/AlOx/Al tunnel junctions with thinner barriers, and in thicker barriers we observe weak points which facilitate single-electron currents. We also find that the disordered nature of the amorphous barrier results in significant variations in the transport properties. We also determine the current-phase phase relationship in our atomistic structures, finding that devices with with pinholes and weak links cause a deviation from the ideal sinusoidal Josephson relationship.
About the presenter
Karen Bayros is a PhD student working with CI Jared Cole and AI Jackson Smith at RMIT where she models current flow through dielectric barriers in superconducting quantum bits. The influence of defects and imperfections can limit the dissipationless flow-through devices comprised of these barriers, and Karen uses advanced computational models to understand the interplay between the molecular structure and the electrical response, within FLEET’s Research theme 1: topological materials.