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arXiv · 2509.04776

Transmon-assisted high-fidelity controlled-Z gates for integer fluxonium qubits

J. -H. Wang·H. Xiong·J. -Z. Yang·H. -Y. Zhang·Y. -P. Song·L. -M. Duan
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Abstract

Fluxoniums, as partially-protected superconducting qubits are promising to be employed to build high-performance large-scale quantum processor. The recently proposed ``integer fluxonium" operates at zero external flux bias, with a frequency of approximately 3 GHz. Single-qubit gate fidelity has been demonstrated to exceed $99.9\%$, while two-qubit gate schemes and scalable architectures remain underexplored. In this work, we investigate a fluxonium-transmon-fluxonium (FTF) coupling architecture using integer fluxoniums. We first confirm suppression of $ZZ$ interaction in the FTF system and then propose two high-fidelity controlled-$Z$ (CZ) gate schemes utilizing the coupler control: a flux-activated adiabatic gate scheme and a microwave-activated non-adiabatic gate scheme. Both schemes are capable of achieving low coherent error on the order of $1 \times 10^{-6}$ within gate durations of several tens of nanoseconds. Additionally, we discuss a hybrid circuit system in which an integer fluxonium is coupled to a conventional fluxonium through a transmon coupler. Our proposal provides insights for future implementations of large-scale quantum circuits based on integer fluxonium devices.

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J. -H. Wang, H. Xiong, J. -Z. Yang, H. -Y. Zhang, Y. -P. Song, L. -M. Duan. 2025-09-05. Transmon-assisted high-fidelity controlled-Z gates for integer fluxonium qubits. https://doi.org/10.1103/qmds-z7gb

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