Journal Article

Systematic improvements in transmon qubit coherence enabled by niobium surface encapsulation

Nekrashevich, Ivan, Kopas, Cameron J., Zhu, Shaojiang, Vu, Kim, Zanten, David van, Sauls, James A., Pappas, David P., Krasnikova, Yulia, Miller, Duncan, You, Xinyuan, Hersam, Mark C., Murthy, Akshay A., Roy, Tanay, Lecocq, Florent, Bal, Mustafa, Crisa, Francesco, Kramer, Matthew J., Romanenko, Alexander, Bafia, Daniel, Reagor, Matthew J., Mutus, Josh Y., Lachman, Ella O., Pilipenko, Roman, Pritchard, P. Graham, Goronzy, Dominic P., Rondinelli, James M., Torres-Castanedo, Carlos G., Zasadzinski, John, Cansizoglu, Hilal, Bedzyk, Michael J., Grassellino, Anna, Huang, Ziwen, Lee, Jaeyel, Koch, Jens, Marshall, Jayss, Zhou, Lin, Lunin, Andrei, Yadavalli, Kameshwar, Dravid, Vinayak P., Oh, Jin-Su

2024

Overview

We present a transmon qubit fabrication technique that yields systematic improvements in T 1 relaxation times. We encapsulate the surface of niobium and prevent the formation of its lossy surface oxide. By maintaining the same superconducting metal and only varying the surface, this comparative investigation examining different capping materials, such as tantalum, aluminum, titanium nitride, and gold, as well as substrates across different qubit foundries demonstrates the detrimental impact that niobium oxides have on coherence times of superconducting qubits, compared to native oxides of tantalum, aluminum or titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T 1 relaxation times 2–5 times longer than baseline qubit devices with native niobium oxides. When capping niobium with tantalum, we obtain median qubit lifetimes above 300 μs, with maximum values up to 600 μs. Our comparative structural and chemical analysis provides insight into why amorphous niobium oxides may induce higher losses compared to other amorphous oxides.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Partner Journals,Nature Portfolio
• Subject: 639/301/119/1003 / 639/766/119/1003 / 639/766/483/2802 / Aluminum / Analytical chemistry / Classical and Quantum Gravitation / CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS / Electrons / Geometry / Oxides / Physics / Physics and Astronomy / Quantum Computing / Quantum Field Theories / Quantum Information Technology / Quantum Physics / Relativity Theory / Spintronics / String Theory / Tantalum / Titanium