Coherent superconducting qubits from a subtractive junction fabrication process

Stehli, A., Brehm, J. D., Wolz, T., Baity, P. , Danilin, S. , Seferai, V. , Rotzinger, H., Ustinov, A. V. and Weides, M. (2020) Coherent superconducting qubits from a subtractive junction fabrication process. Applied Physics Letters, 117(12), 124005. (doi: 10.1063/5.0023533)

Abstract

Josephson tunnel junctions are the centerpiece of almost any superconducting electronic circuit, including qubits. Typically, the junctions for qubits are fabricated using shadow evaporation techniques to reduce dielectric loss contributions from the superconducting film interfaces. In recent years, however, sub-micrometer scale overlap junctions have started to attract attention. Compared to shadow mask techniques, neither an angle dependent deposition nor free-standing bridges or overlaps are needed, which are significant limitations for wafer-scale processing. This comes at the cost of breaking the vacuum during fabrication, but simplifies integration in multi-layered circuits and implementation of vastly different junction sizes and enables fabrication on a larger scale in an industrially standardized process. In this work, we demonstrate the feasibility of a subtractive process for the fabrication of overlap junctions. In an array of test contacts, we find low aging of the average normal state resistance of only 1.6% over 6 months. We evaluate the coherence properties of the junctions by employing them in superconducting transmon qubits. In time domain experiments, we find that both, the qubit life- and coherence time of our best device, are, on average, greater than 20μs. Finally, we discuss potential improvements to our technique. This work paves the way toward a more standardized process flow with advanced materials and growth processes, and constitutes an important step for the large scale fabrication of superconducting quantum circuits.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Seferai, Valentino and Weides, Professor Martin and Danilin, Dr Sergey and Baity, Dr Paul
• Authors: Stehli, A., Brehm, J. D., Wolz, T., Baity, P., Danilin, S., Seferai, V., Rotzinger, H., Ustinov, A. V., and Weides, M.
• College/School: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Journal Name: Applied Physics Letters
• Publisher: AIP Publishing
• ISSN: 0003-6951
• ISSN (Online): 1077-3118
• Published Online: 24 September 2020
• Copyright Holders: Copyright © 2020 AIP Publishing
• First Published: First published in Applied Physics Letters 117(12): 124005
• Publisher Policy: Reproduced in accordance with the publisher copyright policy

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
306059		EPSRC Hub for Quantum Computing and Simulation	Martin Weides	Engineering and Physical Sciences Research Council (EPSRC)	EP/T001062/1	ENG - Electronics & Nanoscale Engineering