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Scalable fluxonium-transmon architecture for error-corrected quantum processors

Lukas Heunisch1,*, Longxiang Huang2,3, Timo Eckstein1, Stephan Tasler1, Johannes Schirk2,3, Florian Wallner2,3, Verena Feulner1, Bijita Sarma1, Klaus Liegener2,3 et al.

Christian M. F. Schneider2,3, Stefan Filipp2,3,4, and Michael J. Hartmann1,†

  • *Contact author: lukas.heunisch@fau.de
  • †Contact author: michael.j.hartmann@fau.de
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Phys. Rev. Research 8, 033245 – Published 28 August, 2026

DOI: https://doi.org/10.1103/ts1j-nfg1

Abstract

We propose a hybrid quantum computing architecture composed of alternating fluxonium and transmon qubits, which are coupled via transmon tunable couplers. We show that this system offers excellent scaling properties, characterized by engineered zero ZZ crosstalk in the idle regime, a substantial reduction of level-crowding challenges through the alternating arrangement of different qubit types within the lattice, and parameter regimes that circumvent the capacitive loading problem commonly associated with fluxoniums. In numerical simulations, we show a parametrically driven CZ gate that achieves a closed-system infidelity that is orders of magnitude below the coherence limit for gate durations ≳30ns using a two-tone flux pulse on the tunable coupler. Furthermore, we show that this gate scheme retains its fidelity in the presence of multiple spectator qubits, making it a scalable solution for large lattices. Moreover, for the implementation of error correcting codes, our approach can leverage the long coherence times and large nonlinearities of fluxoniums as data qubits, while fixed-frequency transmons with established readout techniques can serve as measurement ancillae.

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Phys. Rev. Research 8, 033245– Published 28 August, 2026
  • Received 17 September 2025
  • Revised 15 April 2026
  • Accepted 7 July 2026
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