Crosstalk in multiqubit fluxonium architectures with transmon couplers
Martijn F.S. Zwanenburg (TU Delft - QRD/Andersen Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
Christian Kraglund Andersen (TU Delft - QRD/Andersen Lab, TU Delft - QuTech Advanced Research Centre, TU Delft - Applied Sciences, Kavli institute of nanoscience Delft)
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Abstract
In recent years, several architectures have been proposed for implementing two-qubit operations on fluxonium superconducting qubits. A particularly promising approach, which was demonstrated experimentally by Refs. [L. Ding et al. Phys. Rev. X13, 031035 (2026) PRXHAE 2160-3308 10.1103/PhysRevX.13.031035, S. Singh et al. Phys. Rev. Appl.25, 024020 (2026) PRAHB2 2331-7019 10.1103/yxf3-jtx5], employs a transmon superconducting qubit as a tunable coupler between the fluxonium qubits. These experiments have shown that the transmon coupler enables fast, high-fidelity two-qubit operations while suppressing unwanted ZZ crosstalk between the fluxonium qubits. In this work, we numerically study the scalability of this architecture. We find that, when trivially scaling this architecture, crosstalk from spectator qubits limits the gate fidelity to below 90%. We show that these spectator errors can be reduced to below 10−4 by reducing the coupling strength and by dynamically tuning transmons that are not used for a two-qubit operation to an off position. We further investigate the resilience of the operation to direct capacitive coupling between the transmon couplers and to microwave crosstalk.
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