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The superconducting quasicharge qubit

Author

Listed:
  • Ivan V. Pechenezhskiy

    (University of Maryland)

  • Raymond A. Mencia

    (University of Maryland)

  • Long B. Nguyen

    (University of Maryland)

  • Yen-Hsiang Lin

    (University of Maryland
    National Tsinghua University)

  • Vladimir E. Manucharyan

    (University of Maryland)

Abstract

The non-dissipative nonlinearity of Josephson junctions1 converts macroscopic superconducting circuits into artificial atoms2, enabling some of the best-controlled qubits today3,4. Three fundamental types of superconducting qubit are known5, each reflecting a distinct behaviour of quantum fluctuations in a Cooper pair condensate: single-charge tunnelling (charge qubit6,7), single-flux tunnelling (flux qubit8) and phase oscillations (phase qubit9 or transmon10). Yet, the dual nature of charge and flux suggests that circuit atoms must come in pairs. Here we introduce the missing superconducting qubit, ‘blochnium’, which exploits a coherent insulating response of a single Josephson junction that emerges from the extension of phase fluctuations beyond 2π (refs. 11–14). Evidence for such an effect has been found in out-of-equilibrium direct-current transport through junctions connected to high-impedance leads15–19, although a full consensus on the existence of extended phase fluctuations is so far absent20–22. We shunt a weak junction with an extremely high inductance—the key technological innovation in our experiment—and measure the radiofrequency excitation spectrum as a function of external magnetic flux through the resulting loop. The insulating character of the junction is manifested by the vanishing flux sensitivity of the qubit transition between the ground state and the first excited state, which recovers rapidly for transitions to higher-energy states. The spectrum agrees with a duality mapping of blochnium onto a transmon, which replaces the external flux by the offset charge and introduces a new collective quasicharge variable instead of the superconducting phase23,24. Our findings may motivate the exploration of macroscopic quantum dynamics in ultrahigh-impedance circuits, with potential applications in quantum computing and metrology.

Suggested Citation

  • Ivan V. Pechenezhskiy & Raymond A. Mencia & Long B. Nguyen & Yen-Hsiang Lin & Vladimir E. Manucharyan, 2020. "The superconducting quasicharge qubit," Nature, Nature, vol. 585(7825), pages 368-371, September.
  • Handle: RePEc:nat:nature:v:585:y:2020:i:7825:d:10.1038_s41586-020-2687-9
    DOI: 10.1038/s41586-020-2687-9
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    Citations

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    Cited by:

    1. Fabian Kaap & Christoph Kissling & Victor Gaydamachenko & Lukas Grünhaupt & Sergey Lotkhov, 2024. "Demonstration of dual Shapiro steps in small Josephson junctions," Nature Communications, Nature, vol. 15(1), pages 1-6, December.
    2. Johannes Koch & Geram R. Hunanyan & Till Ockenfels & Enrique Rico & Enrique Solano & Martin Weitz, 2023. "Quantum Rabi dynamics of trapped atoms far in the deep strong coupling regime," Nature Communications, Nature, vol. 14(1), pages 1-9, December.
    3. F. Hassani & M. Peruzzo & L. N. Kapoor & A. Trioni & M. Zemlicka & J. M. Fink, 2023. "Inductively shunted transmons exhibit noise insensitive plasmon states and a fluxon decay exceeding 3 hours," Nature Communications, Nature, vol. 14(1), pages 1-10, December.
    4. Diego Subero & Olivier Maillet & Dmitry S. Golubev & George Thomas & Joonas T. Peltonen & Bayan Karimi & Marco Marín-Suárez & Alfredo Levy Yeyati & Rafael Sánchez & Sunghun Park & Jukka P. Pekola, 2023. "Bolometric detection of Josephson inductance in a highly resistive environment," Nature Communications, Nature, vol. 14(1), pages 1-8, December.
    5. Eric Hyyppä & Suman Kundu & Chun Fai Chan & András Gunyhó & Juho Hotari & David Janzso & Kristinn Juliusson & Olavi Kiuru & Janne Kotilahti & Alessandro Landra & Wei Liu & Fabian Marxer & Akseli Mäkin, 2022. "Unimon qubit," Nature Communications, Nature, vol. 13(1), pages 1-14, December.

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