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Crosstalk in multiqubit fluxonium architectures with transmon couplers

Martijn F. S. Zwanenburg* and Christian Kraglund Andersen†

  • *Contact author: m.f.s.zwanenburg@tudelft.nl
  • †Contact author: c.k.andersen@tudelft.nl
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Phys. Rev. Applied 26, 024088 – Published 31 August, 2026

DOI: https://doi.org/10.1103/rf7g-md41

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. X 13, 031035 (2023), S. Singh et al. Phys. Rev. Appl. 25, 024020 (2026)], 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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References (39)

  1. L. Ding, M. Hays, Y. Sung, B. Kannan, J. An, A. Di Paolo, A. H. Karamlou, T. M. Hazard, K. Azar, D. K. Kim et al., High-fidelity, frequency-flexible two-qubit fluxonium gates with a transmon coupler, Phys. Rev. X 13, 031035 (2023).
  2. S. Singh, E. Y. Huang, J. Hu, F. Yilmaz, M. F. S. Zwanenburg, P. Kumaravadivel, S. Wang, T. V. Stefanski, and C. K. Andersen, Fast microwave-driven two-qubit gates between fluxonium qubits with a transmon coupler, Phys. Rev. Appl. 25, 024020 (2026).
  3. K. N. Nesterov, I. V. Pechenezhskiy, C. Wang, V. E. Manucharyan, and M. G. Vavilov, Microwave-activated controlled-Z gate for fixed-frequency fluxonium qubits, Phys. Rev. A 98, 030301(R) (2018).
  4. I. N. Moskalenko, I. A. Simakov, N. N. Abramov, A. A. Grigorev, D. O. Moskalev, A. A. Pishchimova, N. S. Smirnov, E. V. Zikiy, I. A. Rodionov, and I. S. Besedin, High fidelity two-qubit gates on fluxoniums using a tunable coupler, npj Quantum Inf. 8, 130 (2022).
  5. E. Dogan, D. Rosenstock, L. Le Guevel, H. Xiong, R. A. Mencia, A. Somoroff, K. N. Nesterov, M. G. Vavilov, V. E. Manucharyan, and C. Wang, Two-fluxonium cross-resonance gate, Phys. Rev. Appl. 20, 024011 (2023).
  6. W.-J. Lin, H. Cho, Y. Chen, M. G. Vavilov, C. Wang, and V. E. Manucharyan, 24 days-stable CNOT gate on fluxonium qubits with over 99.9% fidelity, PRX Quantum 6, 010349 (2025).
  7. P. Zhao, G. Zhao, S. Li, C. Zha, and M. Gong, Scalable fluxonium-qubit architecture with tunable interactions between noncomputational levels, Phys. Rev. Appl. 25, 044072 (2026).
  8. D. A. Rower, L. Ding, H. Zhang, M. Hays, J. An, P. M. Harrington, I. T. Rosen, J. M. Gertler, T. M. Hazard, B. M. Niedzielski et al., Suppressing counter-rotating errors for fast single-qubit gates with fluxonium, PRX Quantum 5, 040342 (2024).
  9. M. F. S. Zwanenburg, S. Singh, E. Y. Huang, F. Yilmaz, T. V. Stefanski, J. Hu, P. Kumaravadivel, and C. K. Andersen, Single-qubit gates beyond the rotating-wave approximation for strongly anharmonic low-frequency qubits, Phys. Rev. Research 7, 043290 (2025).
  10. T. Wang, F. Wu, F. Wang, X. Ma, G. Zhang, J. Chen, H. Deng, R. Gao, R. Hu, L. Ma et al., Efficient initialization of fluxonium qubits based on auxiliary energy levels, Phys. Rev. Lett. 132, 230601 (2024).
  11. T. V. Stefanski, F. Yilmaz, E. Y. Huang, M. F. S. Zwanenburg, S. Singh, S. Wang, L. J. Splitthoff, and C. K. Andersen, Improved fluxonium readout through dynamic flux pulsing, arXiv:2411.13437.
  12. K. N. Nesterov and I. V. Pechenezhskiy, Measurement-induced state transitions in dispersive qubit-readout schemes, Phys. Rev. Appl. 22, 064038 (2024).
  13. V. E. Manucharyan, J. Koch, L. I. Glazman, and M. H. Devoret, Fluxonium: Single cooper-pair circuit free of charge offsets, Science 326, 113 (2009).
  14. S. Krinner, S. Lazar, A. Remm, C. K. Andersen, N. Lacroix, G. J. Norris, C. Hellings, M. Gabureac, C. Eichler, and A. Wallraff, Benchmarking coherent errors in controlled-phase gates due to spectator qubits, Phys. Rev. Appl. 14, 024042 (2020).
  15. N. Sundaresan, I. Lauer, E. Pritchett, E. Magesan, P. Jurcevic, and J. M. Gambetta, Reducing unitary and spectator errors in cross resonance with optimized rotary echoes, PRX Quantum 1, 020318 (2020).
  16. D. M. Zajac, J. Stehlik, D. L. Underwood, T. Phung, J. Blair, S. Carnevale, D. Klaus, G. A. Keefe, A. Carniol, M. Kumph, M. Steffen, and O. E. Dial, Spectator errors in tunable coupling architectures, arXiv:2108.11221.
  17. S. Krinner, N. Lacroix, A. Remm, A. Di Paolo, E. Genois, C. Leroux, C. Hellings, S. Lazar, F. Swiadek, J. Herrmann, G. J. Norris, C. K. Andersen, M. Müller, A. Blais, C. Eichler, and A. Wallraff, Realizing repeated quantum error correction in a distance-three surface code, Nature (London) 605, 669 (2022).
  18. J. F. Marques, B. M. Varbanov, M. S. Moreira, H. Ali, N. Muthusubramanian, C. Zachariadis, F. Battistel, M. Beekman, N. Haider, W. Vlothuizen, A. Bruno, B. M. Terhal, and L. DiCarlo, Logical-qubit operations in an error-detecting surface code, Nat. Phys. 18, 80 (2022).
  19. Google Quantum AI, Suppressing quantum errors by scaling a surface code logical qubit, Nature (London) 614, 676 (2023).
  20. Google Quantum AI and Collaborators, Quantum error correction below the surface code threshold, Nature (London) 638, 920 (2025).
  21. S. Gonzaléz-García, A. Szasz, A. Pagano, D. Kafri, G. Vidal, and A. Di Paolo, Multi-target density matrix renormalization group X algorithm and its application to circuit quantum electrodynamics, arXiv:2506.24109.
  22. F. Lange, L. Heunisch, H. Fehske, D. P. DiVincenzo, and M. J. Hartmann, Cross-talk in superconducting qubit lattices with tunable couplers—comparing transmon and fluxonium architectures, Quantum Sci. Tehnol. 11, 015020 (2026).
  23. J. Koch, T. M. Yu, J. Gambetta, A. A. Houck, D. I. Schuster, J. Majer, A. Blais, M. H. Devoret, S. M. Girvin, and R. J. Schoelkopf, Charge-insensitive qubit design derived from the cooper pair box, Phys. Rev. A 76, 042319 (2007).
  24. F. Yan, P. Krantz, Y. Sung, M. Kjaergaard, D. L. Campbell, T. P. Orlando, S. Gustavsson, and W. D. Oliver, Tunable coupling scheme for implementing high-fidelity two-qubit gates, Phys. Rev. Appl. 10, 054062 (2018).
  25. J. An, H. Zhang, Q. Ding, L. Ding, Y. Sung, R. Winik, J. Kim, I. T. Rosen, K. Azar, P. Piñero et al., ZZ-free two-transmon CZ gate mediated by a fluxonium coupler, Phys. Rev. Appl. 26, 014076 (2026).
  26. U. Schollwöck, The density-matrix renormalization group in the age of matrix product states, Ann. Phys. (Amsterdam) 326, 96 (2011).
  27. R. Orús, A practical introduction to tensor networks: Matrix product states and projected entangled pair states, Ann. Phys. (Amsterdam) 349, 117 (2014).
  28. V. Khemani, F. Pollmann, and S. L. Sondhi, Obtaining highly excited eigenstates of many-body localized Hamiltonians by the density matrix renormalization group approach, Phys. Rev. Lett. 116, 247204 (2016).
  29. F. Motzoi, J. M. Gambetta, P. Rebentrost, and F. K. Wilhelm, Simple pulses for elimination of leakage in weakly nonlinear qubits, Phys. Rev. Lett. 103, 110501 (2009).
  30. J. M. Gambetta, F. Motzoi, S. T. Merkel, and F. K. Wilhelm, Analytic control methods for high-fidelity unitary operations in a weakly nonlinear oscillator, Phys. Rev. A 83, 012308 (2011).
  31. E. Hyyppä, A. Vepsäläinen, M. Papič, C. F. Chan, S. Inel, A. Landra, W. Liu, J. Luus, F. Marxer, C. Ockeloen-Korppi, S. Orbell, B. Tarasinski, and J. Heinsoo, Reducing leakage of single-qubit gates for superconducting quantum processors using analytical control pulse envelopes, PRX Quantum 5, 030353 (2024).
  32. D. Gottesman, Quantum fault tolerance in small experiments, arXiv:1610.03507.
  33. M. Takita, A. D. Córcoles, E. Magesan, B. Abdo, M. Brink, A. Cross, J. M. Chow, and J. M. Gambetta, Demonstration of weight-four parity measurements in the surface code architecture, Phys. Rev. Lett. 117, 210505 (2016).
  34. Delft High Performance Computing Center (DHPC, DelftBlue supercomputer (phase 2) (2024).
  35. Data repository, 10.4121/76fc34c4-6af6-4cc3-b234-ff47d58d6de2.
  36. GitHub repository, https://github.com/andersenqubitlab/crosstalk-in-larger-fluxonium-processors.
  37. C. Lanczos, An iteration method for the solution of the eigenvalue problem of linear differential and integral operators, J. Res. Nat. Bur. Stand. 45, 255 (1950).
  38. Y. Saad, Iterative methods for sparse linear systems (SIAM, Philadelphia, PA, 2003), Chap. 7, pp. 229–258.
  39. R. Okuta, Y. Unno, D. Nishino, S. Hido, and C. Loomis, CuPy: A NumPy-compatible library for NVIDIA GPU calculations, in Proceedings of Workshop on Machine Learning Systems (LearningSys) in The Thirty-first Annual Conference on Neural Information Processing Systems (NIPS) (2017).

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Phys. Rev. Applied 26, 024088– Published 31 August, 2026
  • Received 31 March 2026
  • Revised 29 June 2026
  • Accepted 27 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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