Seminar Speaker: Peter Sushko, PNNL

Towards Atomic Precision in Superconducting Qubits: Mechanisms of Ta Oxidation and Strategies for Oxidation Suppression

Abstract

Coherence times of transmon devices can be affected by oxidation of the components made of superconducting metals, such as Nb and Ta. Spontaneous oxidation results in the formation of suboxide phases and surface amorphization that contribute to dielectric losses that are primarily attributed to two-level systems within such native oxide layers. Mitigating undesirable effects of surface oxidation requires understanding the mechanisms of interfacial interactions at the atomic scale. We review recent experimental studies that provide new insights into the atomic structure and composition of the native oxide layer and focus on ab initio simulations of the mechanisms of Ta interaction with oxygen. In particular, we consider energetics and pathways of the early stages of the Ta(110) surface oxidation, including propagation of the oxidation front into the Ta subsurface and corresponding electronic structure changes. We also explore strategies for suppressing Ta oxidation with the help of reactive metal coating and discuss models of candidate two-level systems.

Biography

Dr. Peter Sushko is a computational materials scientist at the Physical Sciences Division, Pacific Northwest National Laboratory (PNNL). He received his BSc and MSc degrees in physics from St. Petersburg State University, Russia. He then completed his PhD in physics at University College London (UCL), UK, where he was developing embedded cluster approaches for simulating electronic properties of point defects in ionic materials. In 2008, Dr. Sushko was awarded a Royal Society University Research Fellowship at the London Center for Nanotechnology and UCL Department of Physics and Astronomy, where he became a lecturer and then a Reader. In 2013 he, as a member of a UK-Japan research team, was awarded the Daiwa Adrian Prize for research on functional abundant metal oxides. In 2014, Dr. Sushko joined PNNL as a leader for the Materials Sciences group in the Physical Sciences Division. In 2021 he took over the role of the lead for the DOE Office of Science, Basic Energy Sciences, Materials Sciences and Engineering sector at PNNL. Dr. Sushko’s research is focused on revealing atomic-scale mechanisms of defect formation and transport and predicting the effects of disorder and defects on materials properties and functions. He has published more than 180 peer-reviewed manuscripts on the physical and chemical properties of nanostructured materials and interfacial phenomena.