Gap-Engineered Transmon Qubits for Mitigation Against Quasiparticles

ORAL

Abstract

Non-equilibrium quasiparticles are a source of decoherence for superconducting transmon qubits. To trap quasiparticles and reduce their tunneling rate across the Josephson junction, we gap engineer one electrode of an asymmetric transmon by capping the Al counter-electrode of our junction with Ti, lowering the superconducting gap via the proximity effect. The T1 of a 3D transmon fabricated with this bilayer was found to drop to 1 µs. Similarly, direct IV measurements of these junctions show high sub-gap conductance. However, by adding disorder between the Al and Ti metals in the form of a thin AlOx layer, we can restore the gap to the value of thin film Al and improve the relaxation time to 32 µs. We use these results to inform the design of new transmons with low-gap trapping away from the junction.

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Presenters

  • Zachary Steffen

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

Authors

  • Zachary Steffen

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Haozhi Wang

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Yizhou Huang

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Yi-Hsiang Huang

    • University of Maryland, College Park

  • Kungang Li

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Sudeep K Dutta

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Frederick C Wellstood

    • University of Maryland, College Park; Quantum Materials Center, University of Maryland, College Park
    • University of Maryland, College Park

  • Benjamin S Palmer

    • Laboratory for Physical Sciences; Quantum Materials Center, University of Maryland, College Park
    • Laboratory for Physical Sciences, Quantum Materials Center, University of Maryland
    • Laboratory for Physical Sciences