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Blueprint for a High-Performance Fluxonium Quantum Processor

Long B. Nguyen, Gerwin Koolstra, Yosep Kim, Alexis Morvan, Trevor Chistolini, Shraddha Singh, Konstantin N. Nesterov, Christian Jünger, Larry Chen, Zahra Pedramrazi, Bradley K. Mitchell, John Mark Kreikebaum, Shruti Puri, David I. Santiago, and Irfan Siddiqi
PRX Quantum 3, 037001 – Published 5 August 2022

Abstract

Transforming stand-alone qubits into a functional, general-purpose quantum processing unit requires an architecture where many-body quantum entanglement can be generated and controlled in a coherent, modular, and measurable fashion. Electronic circuits promise a well-developed pathway for large-scale integration once a mature library of quantum-compatible elements have been developed. In the domain of superconducting circuits, fluxonium has recently emerged as a promising qubit due to its high-coherence and large anharmonicity, yet its scalability has not been systematically explored. In this work, we present a blueprint for a high-performance fluxonium-based quantum processor that addresses the challenges of frequency crowding, and both quantum and classical crosstalk. The main ingredients of this architecture include high-anharmonicity circuits, multipath couplers to entangle qubits where spurious longitudinal coupling can be nulled, circuit designs that are compatible with multiplexed microwave circuitry, and strongly coupled readout channels that do not require complex, frequency-sculpted elements to maintain coherence. In addition, we explore robust and resource-efficient protocols for quantum logical operations, then perform numerical simulations to validate the expected performance of this proposed processor with respect to gate fidelity, fabrication yield, and logical error suppression. Lastly, we discuss practical considerations to implement the architecture and achieve the anticipated performance.

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  • Received 27 January 2022
  • Revised 29 June 2022
  • Accepted 5 July 2022
  • Corrected 13 February 2023

DOI:https://doi.org/10.1103/PRXQuantum.3.037001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & TechnologyCondensed Matter, Materials & Applied Physics

Corrections

13 February 2023

Correction: Equation (21) contained a coding error introduced during the production cycle and has been fixed.

Authors & Affiliations

Long B. Nguyen1,2,*, Gerwin Koolstra1,2, Yosep Kim1,2,‡, Alexis Morvan1,2,§, Trevor Chistolini2, Shraddha Singh3,4, Konstantin N. Nesterov5, Christian Jünger1,2, Larry Chen2, Zahra Pedramrazi1,2, Bradley K. Mitchell1,2, John Mark Kreikebaum2,6, Shruti Puri3,4, David I. Santiago1,2, and Irfan Siddiqi1,2,6,†

  • 1Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
  • 2Department of Physics, University of California, Berkeley, California 94720, USA
  • 3Department of Applied Physics, Yale University, New Haven, Connecticut 06511, USA
  • 4Yale Quantum Institute, Yale University, New Haven, Connecticut 06511, USA
  • 5Bleximo Corp., Berkeley, California 94720, USA
  • 6Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

  • *longbnguyen@berkeley.edu
  • irfan_siddiqi@berkeley.edu
  • Current address: Center for Quantum Information, Korea Institute of Science and Technology (KIST), Seoul 02792, Korea.
  • §Current address: Google Quantum AI, Mountain View, CA 94043, USA.

Popular Summary

The development of superconducting hardware toward fault-tolerant quantum computation faces the challenges of crosstalk, frequency crowding, increased design constraints, and operational complexity. These are exacerbated by the weak anharmonicity and unprotected quantum states of the currently mainstream transmon qubits. In this work, we propose and analyze an alternative architecture based on fluxonium circuits that has the potential to circumvent those problems.

After surveying the current research progress on fluxonium, we provide an essential review on the properties of the qubit. Based on these principles, we explore multipath connectivity of qubits with a specific parameters range, demonstrating via numerical simulations that the operational fidelities of the architecture can be better than state-of-the-art results. We extend our investigation toward the fault-tolerance regime using surface code, showing that a large-scale device with square lattice topology can be feasibly constructed with available technologies, resulting in exponential suppression of logical error rates. A practical roadmap is provided as a guide for upcoming experimental efforts.

These promising assessments will both amplify the interest in fluxonium research and motivate similar studies on the scalability of other novel qubits.

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Vol. 3, Iss. 3 — August - October 2022

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