Gralmonium: Granular Aluminum Nano-Junction Fluxonium Qubit

ORAL  · Invited

Abstract

Mesoscopic Josephson junctions (JJs), consisting of overlapping superconducting electrodes separated by a nanometer thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits and are at the heart of state-of-the-art qubits, such as the transmon and fluxonium. Here, we show that in a fluxonium qubit the role of the JJ can also be played by a lithographically defined, self-structured granular aluminum (grAl) nano-junction: a superconductor-insulator-superconductor (SIS) JJ obtained in a single layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from the one of a standard fluxonium qubit. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large grAl nano-junction charging energy in the range of tens of GHz, comparable to its Josephson energy EJ. We measure average energy relaxation times of T1 = 10 µs and Hahn echo coherence times of T2echo = 9 μs. The exponential sensitivity of the gralmonium to the EJ of the grAl nano-junction provides a highly susceptible detector. Indeed, we observe spontaneous jumps of the value of EJ on timescales from milliseconds to days, which offer a powerful diagnostics tool for microscopic defects in superconducting materials.

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Publication: Rieger & Günzler et al., arXiv 2202.01776 (2022),
Nature Materials, in press

Presenters

  • Dennis Rieger

    • PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • Karlsruhe Institute of Technology
    • PHI, Karlsruhe Institute of Technology

Authors

  • Dennis Rieger

    • PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • Karlsruhe Institute of Technology
    • PHI, Karlsruhe Institute of Technology

  • Simon Günzler

    • PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology
    • Karlsruhe Institute of Technology

  • Martin Spiecker

    • PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology

  • Patrick Paluch

    • IQMT and PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)

  • Patrick Winkel

    • PHI, Karlsruhe Institute of Technology, Germany
    • Karlsruhe Institute of Technology (KIT)
    • Karlsruhe Institute of Technology

  • Lothar Hahn

    • IMT, Karlsruhe Institute of Technology

  • Judith K Hohmann

    • IMT, Karlsruhe Institute of Technology

  • Andreas Bacher

    • IMT, Karlsruhe Institute of Technology

  • Wolfgang Wernsdorfer

    • IQMT and PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology
    • Karlsruhe Institute of Technology

  • Ioan M Pop

    • IQMT and PHI, Karlsruhe Institute of Technology, Germany
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology (KIT), Germany
    • Karlsruhe Institute of Technology (KIT)
    • IQMT and PHI, Karlsruhe Institute of Technology
    • Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany