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arXiv · 2608.25503

High-Fidelity Entangled States in a Connectivity-Four Fluxonium Quantum Processor

J. Schirk·N. Bruckmoser·S. M. Taubenberger·F. Wallner·N. J. Glaser·M. Zetzl·L. Huang·I. Tsitsilin·M. Werninghaus·L. Södergren·K. Liegener·C. M. F. Schneider·Stefan Filipp
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Abstract

A central challenge in fluxonium-based quantum processors is the extension of the qubit connectivity to two-dimensional lattices compatible with quantum code-error correction. Here, we present a fluxonium quantum processor that employs lumped-element resonator couplers which realizes, for the first time, a connectivity-four unit cell with suppressed parasitic interactions. We achieve parallel single-qubit gate fidelities exceeding 99.9 % in simultaneous randomized benchmarking experiments, while maintaining residual static ZZ interactions below 1 kHz across all coupled qubit pairs. We implement resonator-induced phase (RIP) gates and benchmark two-qubit gate fidelities exceeding 99 % using interleaved randomized benchmarking. To cancel spectator errors observed in two-qubit operations, we implement a refocused RIP gate, recovering coherent control in the presence of multi-qubit connectivity. Furthermore, we prepare Greenberger-Horne-Zeilinger states of up to five qubits with a tomographic fidelity of 90 %, verifying multi-qubit entanglement within the unit cell. These results establish the fluxonium-resonator-fluxonium architecture as a viable approach to realizing densely connected fluxonium processors and provide a scalable path toward quantum error-correction-compatible processor architectures.

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J. Schirk, N. Bruckmoser, S. M. Taubenberger, F. Wallner, N. J. Glaser, M. Zetzl, L. Huang, I. Tsitsilin, M. Werninghaus, L. Södergren, K. Liegener, C. M. F. Schneider, Stefan Filipp. 2026-08-26. High-Fidelity Entangled States in a Connectivity-Four Fluxonium Quantum Processor. https://arxiv.org/abs/2608.25503

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