Enhanced superconducting qubit performance through ammonium fluoride etch

Cameron J. Kopas*, Dominic P. Goronzy, Thang Pham, Carlos G. Torres Castanedo, Matthew Cheng, Rory Cochrane, Patrick Nast, Ella Lachman, Nikolay Z. Zhelev, André Vallières, Akshay A. Murthy, Jin Su Oh, Lin Zhou, Matthew J. Kramer, Hilal Cansizoglu, Michael J. Bedzyk, Vinayak P. Dravid, Alexander Romanenko, Anna Grassellino, Josh Y. MutusMark C. Hersam, Kameshwar Yadavalli

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The performance of superconducting qubits is often limited by dissipation and two-level systems (TLS) losses. The dominant sources of these losses are believed to originate from amorphous materials and defects at interfaces and surfaces, likely as a result of fabrication processes or ambient exposure. Here, we explore a novel wet chemical surface treatment at the Josephson junction-substrate and the substrate-air interfaces by replacing a buffered oxide etch (BOE) cleaning process with one that uses hydrofluoric acid followed by aqueous ammonium fluoride. We show that the ammonium fluoride etch process results in a statistically significant improvement in median T 1 by ∼ 22 % (p = 0.002), and a reduction in the number of strongly-coupled TLS in the tunable frequency range. Microwave resonator measurements on samples treated with the ammonium fluoride etch after niobium deposition and etching also show ∼ 33 % lower TLS-induced loss tangent compared to the BOE treated samples. As the chemical treatment primarily modifies the Josephson junction-substrate interface and substrate-air interface, we perform targeted chemical and structural characterizations to examine materials differences at these interfaces and identify multiple microscopic changes that could contribute to decreased TLS losses.

Original languageEnglish (US)
Article number045101
JournalMaterials for Quantum Technology
Volume4
Issue number4
DOIs
StatePublished - Dec 1 2024

Funding

This material is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract no. DE-AC02-07CH11359. This work made use of the Rigetti Fab-1 facilities. This work made use of the EPIC and Keck-II facilities of the Northwestern University NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and the Northwestern MRSEC program (NSF DMR-2308691). This work also made use of the QSET facility of the Northwestern University Center for Applied Physics and Superconducting Technologies (CAPST), which has received support from SQMS. The Ames National Laboratory is operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.

Keywords

  • fabrication
  • interfaces
  • superconducting qubits
  • two-level systems

ASJC Scopus subject areas

  • General Materials Science
  • Condensed Matter Physics
  • Atomic and Molecular Physics, and Optics

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