Correlating the quality factor with the deposition temperature of Nb thin films used in superconducting qubits

ORAL

Abstract

Niobium thin films are widely used in transmon qubits for readout resonators, capacitor pads, and coupling lines. Consequently, there is a major effort to correlate the performance with material properties. One of the important parameters of epitaxial growth is the deposition temperature. While there is no correlation with the residual resistivity ratio, RRR, it is determined that lower deposition temperature results in higher transition temperature, Tc, and improved intrinsic mean quality factor, Qi [1]. By using magneto-optical (MO) imaging of the superconducting state, we show a direct correlation between Qi and uniformity of magnetic flux penetration as well as critical current [2, 3]. The quasiparticle spectroscopy using a tunnel-diode resonator (TDR) shows a higher population of quasiparticles in a low Qi film (deposited at a higher temperature). Not only does superfluid density deviate from the exponential BCS behavior at low temperatures, but it also exhibits non-monotonic features suggesting localized in-gap states, perhaps overlapping two-level systems [2, 4]. We conclude that the combined MO and TDR measurements represent a powerful novel tool for rapid characterization of superconducting qubits.

References:

[1] McFadden, Anthony P., et al. "Interface-sensitive microwave loss in superconducting tantalum films sputtered on c-plane sapphire." Physical Review Materials 9.9 (2025): 096201.

[2] Joshi, Kamal R., et al. "Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting qubits." Physical Review Applied 20.2 (2023): 024031.

[3] Oh, Jin-Su, et al. "Exploring the relationship between deposition method, microstructure, and performance of Nb/Si-based superconducting coplanar waveguide resonators." Acta Materialia 276 (2024): 120153.

[4] Ghimire, Sunil, et al. "Quasiparticle spectroscopy in technologically relevant niobium using London penetration depth measurements: experiment and theory." Materials for Quantum Technology 4.4 (2024): 045201.

*This work was 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. 89243024CSC000002. Fermilab is operated by Fermi Forward Discovery Group, LLC under Contract No. 89243024CSC000002 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. The work was performed at Ames National Laboratory, operated for the U.S. Department of Energy by Iowa State University under Contract No. DE-AC02-07CH11358.

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Presenters

  • Amlan Datta

    • Ames National Laboratory, Iowa State University

Authors

  • Amlan Datta

    • Ames National Laboratory, Iowa State University

  • Kamal R Joshi

    • Iowa State University
    • Ames National Laboratory

  • Bicky Singh Moirangthem

    • Ames National Laboratory, Iowa State University
    • Iowa State University

  • Tony McFadden

    • National Institute of Standards and Technology Boulder
    • National Institute of Standards and Technology
    • National Institute of Standards and Technology, Boulder CO 80305
    • National Institute of Standards and Technology, Boulder, Colorado 80305, USA
    • National Institute of Standards and Technology (NIST)
    • University of California, Santa Barbara
    • National Institute of Standards and Technology, Boulder

  • Florent Lecocq

    • National Institute of Standards and Technology, University of Colorado Boulder
    • National Institute of Standards and Technology
    • National Institute of Standards and Technology Boulder
    • National Institute of Standards and Technology, Boulder, Colorado 80305, USA
    • National Institute of Standards and Technology Boulder, University of Colorado Boulder

  • Ray W Simmonds

    • National Institute of Standards and Technology, University of Colorado Boulder
    • National Institute of Standards and Technology
    • National Institute of Standards and Technology Boulder
    • The Global Coherence Project

  • Matthew J Kramer

    • Ames National Laboratory
    • Ames Laboratory, Ames IA 50011
    • Ames Laboratory

  • Makariy A Tanatar

    • Ames National Laboratory

  • Ruslan Prozorov

    • Ames National Laboratory