Abstract
The entanglement of microwave photons and spin qubits in silicon represents an important step forwards for quantum information processing using semiconductor quantum dots. Such hybrid spin circuit quantum electrodynamics experiments have been achieved by delocalizing spins in a double quantum dot with spin–orbit interactions to produce a flopping-mode spin qubit with a substantial electric dipole moment. Unfortunately, demonstrations of these qubits have not shown the coherence properties necessary for them to be used as practical single qubits. Here we present a flopping-mode hole-spin qubit in a silicon nanowire coupled to a high-impedance niobium nitride microwave read-out resonator. We report Rabi frequencies exceeding 100 MHz with coherence times in the microsecond range, resulting in a single-gate quality factor of 380. This establishes the speed and reliability of flopping-mode spin qubits. Moreover, using the large frequency tunability of the qubit, we find that radiative decay is the main relaxation channel in our experiment and argue that photon shot noise is the main source of dephasing. These results indicate that optimized microwave engineering can unlock the potential of flopping-mode spin qubits in hybrid circuit quantum electrodynamics architectures and offer a scalable and robust platform for fast and coherent spin qubits with strong coupling to microwave photons.
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Data availability
The datasets generated and analysed during the current study are available via Zenodo at https://doi.org/10.5281/zenodo.18683389 (ref. 52).
Code availability
The code used to analyse the datasets are available via Zenodo at https://doi.org/10.5281/zenodo.18683389 (ref. 52).
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Acknowledgements
We thank J.-L. Thomassin and F. Gustavo for help in the fabrication of the NbN circuitry and M. Boujard and I. Matei for technical support in the laboratory. S. De Franceschi is acknowledged for fruitful discussions and careful proofreading of the paper. We are grateful to Y.-M. Niquet for insightful discussions, and we also thank C. Winkelmann for proofreading the paper. This research has been supported by the European Union’s Horizon 2020 research and innovation programme (Grant Agreement Nos. 951852 (QLSI project), 810504 (ERC project QuCube), 759388 (ERC project LONGSPIN) and. 101174557 (QLSI2)) and by the National Strategy France 2030 (Projects PEPR PRESQUILE ANR-22-PETQ-0002 and PEPR MiraclQ ANR-23-PETQ-0003). S.Z. acknowledges support from the spin–photon PEPR chair. J.C.A.-U. is supported by the Spanish Ministry of Science, innovation and Universities (Grant Nos. PID2023- 148257NA-I00 and RYC2022-037527-I).
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C.X.Y. fabricated the NbN circuitry with help from S.Z. L.N. performed the measurements with the help of S.Z. L.N. analysed the data with input from R.M., É.D. and S.Z. J.C.A.-U. developed the theoretical model and helped in the interpretation of the data. L.N., R.M. and S.Z. co-wrote the Article with input from all authors. H.N. and B.B. were responsible for the front-end fabrication of the device. S.Z. supervised the work.
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Noirot, L., Yu, C.X., Abadillo-Uriel, J.C. et al. Coherence of a hole-spin flopping-mode qubit in a circuit quantum electrodynamics environment. Nat. Phys. (2026). https://doi.org/10.1038/s41567-026-03262-y
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DOI: https://doi.org/10.1038/s41567-026-03262-y
