Scalable Fluxonium-Transmon Architecture for Error Corrected Quantum Processors

arXiv:2508.09267v2 Announce Type: replace Abstract: We propose a hybrid quantum computing architecture composed of alternating fluxonium and transmon qubits, that 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 $\gtrsim 30\,\rm{ns}$ using a two-tone flux pulse on the tunable coupler. Furthermore, we show that this gate scheme retains its fidelity in the presence of 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 non-linearities of fluxoniums as data qubits, while fixed-frequency transmons with established readout techniques can serve as measurement ancillas.

Authors:Lukas Heunisch, Longxiang Huang, Timo Eckstein, Stephan Tasler, Johannes Schirk, Florian Wallner, Verena Feulner, Bijita Sarma, Klaus Liegener, Christian M. F. Schneider, Stefan Filipp, Michael J. Hartmann

Abstract:We propose a hybrid quantum computing architecture composed of alternating fluxonium and transmon qubits, that 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 $\gtrsim 30\,\rm{ns}$ using a two-tone flux pulse on the tunable coupler. Furthermore, we show that this gate scheme retains its fidelity in the presence of 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 non-linearities of fluxoniums as data qubits, while fixed-frequency transmons with established readout techniques can serve as measurement ancillas.

arXiv:2508.09267 [quant-ph]

(or arXiv:2508.09267v2 [quant-ph] for this version)

Phys. Rev. Research 8, 033245 (2026)

https://doi.org/10.1103/ts1j-nfg1 DOI(s) linking to related resources

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Scalable Fluxonium-Transmon Architecture for Error Corrected Quantum Processors

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