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  • Featured in Physics
  • Open Access

Operating Semiconductor Qubits without Individual Barrier Gates

Alexander S. Ivlev1,*, Damien R. Crielaard1,*, Marcel Meyer1, William I. L. Lawrie1, Nico W. Hendrickx1, Amir Sammak2, Yuta Matsumoto1, Lieven M. K. Vandersypen1, Giordano Scappucci1 et al.

Corentin Déprez1 and Menno Veldhorst1,†

  • *These authors contributed equally to this work.
  • †Contact author: m.veldhorst@tudelft.nl
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Phys. Rev. X 15, 031042 – Published 14 August, 2025

DOI: https://doi.org/10.1103/xhq3-4jxz

Abstract

Semiconductor spin qubits have emerged as a promising platform for quantum computing, following a significant improvement in their control fidelities over recent years. Increasing the qubit count remains challenging, beginning with the fabrication of small features and complex fan-outs. A particular challenge has been formed by the need for individual barrier gates to control the exchange interaction between adjacent spin qubits. Here, we propose a method to vary two-qubit interactions without applying pulses on individual barrier gates while also remaining insensitive to detuning noise in first order. Experimentally we find that changing plunger gate voltages over 300 mV can tune the exchange energy J from 100 kHz to 60 MHz. This allows us to perform two-qubit operations without changing the barrier gate voltage. Based on these findings we conceptualize a spin qubit architecture without individual barrier gates, simplifying the fabrication while maintaining the control necessary for universal quantum computation.

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synopsis

Reducing the Number of Wires on a Quantum Chip

Published 14 August, 2025

Experiments show that one of the standard electrode types for semiconductor-based quantum processors isn’t needed.

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Popular Summary

Quantum computers could eventually solve problems far beyond the reach of classical computers. But to make large-scale quantum systems possible, we need to drastically increase the number of qubits. Spins in gate-defined quantum dots—tiny regions in semiconductors where individual electrons are trapped—are a strong candidate for this scaling. However, controlling interactions between these qubits requires a dense web of wiring. In our study, we present and experimentally validate a new method that controls interactions between spins in quantum dots without using individual barrier gate pulses. This approach reduces the number of control lines per quantum dot by a factor of 3 and eliminates the need to control barrier gates individually.

Instead of adjusting the barrier between two qubits directly, we tune the depth of the potential wells at the qubits themselves. This indirect method still changes the effective tunnel barrier between qubits, enabling or disabling their interaction as needed. Our experiments show that this method achieves a strong 600-fold difference in interaction strengths between the “on” and “off” states for two-qubit interactions, without lowering qubit performance. This on-off ratio matches that of state-of-the-art traditional control methods. Our method also supports universal quantum operations, meaning it can be used to perform any quantum computation, all without needing separate lines for each barrier gate. As a result, many of these gates can be merged into one, significantly simplifying the architecture.

Expanding our approach to a merged-barrier architecture would open a path toward more scalable quantum dot arrays. By reducing the complexity of wiring and control, our method helps overcome a key bottleneck in quantum hardware development.

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References (60)

  1. Y. Kim, A. Eddins, S. Anand, K. X. Wei, E. van den Berg, S. Rosenblatt, H. Nayfeh, Y. Wu, M. Zaletel, K. Temme, and A. Kandala, Evidence for the utility of quantum computing before fault tolerance, Nature (London) 618, 500 (2023).
  2. M. DeCross et al., Computational power of random quantum circuits in arbitrary geometries, Phys. Rev. X 15, 021052 (2025).
  3. D. Bluvstein et al., Logical quantum processor based on reconfigurable atom arrays, Nature (London) 626, 58 (2024).
  4. R. Acharya et al. (Google Quantum AI and Collaborators), Quantum error correction below the surface code threshold, Nature (London) 638, 920 (2025).
  5. N. W. Hendrickx, W. I. L. Lawrie, M. Russ, F. van Riggelen, S. L. de Snoo, R. N. Schouten, A. Sammak, G. Scappucci, and M. Veldhorst, A four-qubit germanium quantum processor, Nature (London) 591, 580 (2021).
  6. S. G. J. Philips, M. T. Mądzik, S. V. Amitonov, S. L. De Snoo, M. Russ, N. Kalhor, C. Volk, W. I. L. Lawrie, D. Brousse, L. Tryputen, B. P. Wuetz, A. Sammak, M. Veldhorst, G. Scappucci, and L. M. K. Vandersypen, Universal control of a six-qubit quantum processor in silicon, Nature (London) 609, 919 (2022).
  7. H. C. George et al., 12-spin-qubit arrays fabricated on a 300 mm semiconductor manufacturing line, Nano Lett. 25, 793 (2025).
  8. A. Noiri, K. Takeda, T. Nakajima, T. Kobayashi, A. Sammak, G. Scappucci, and S. Tarucha, Fast universal quantum gate above the fault-tolerance threshold in silicon, Nature (London) 601, 338 (2022).
  9. X. Xue, M. Russ, N. Samkharadze, B. Undseth, A. Sammak, G. Scappucci, and L. M. K. Vandersypen, Quantum logic with spin qubits crossing the surface code threshold, Nature (London) 601, 343 (2022).
  10. A. R. Mills, C. R. Guinn, M. J. Gullans, A. J. Sigillito, M. M. Feldman, E. Nielsen, and J. R. Petta, Two-qubit silicon quantum processor with operation fidelity exceeding 99%, Sci. Adv. 8, eabn5130 (2022).
  11. C.-A. Wang, V. John, H. Tidjani, C. X. Yu, A. S. Ivlev, C. Déprez, F. Van Riggelen-Doelman, B. D. Woods, N. W. Hendrickx, W. I. L. Lawrie, L. E. A. Stehouwer, S. D. Oosterhout, A. Sammak, M. Friesen, G. Scappucci, S. L. De Snoo, M. Rimbach-Russ, F. Borsoi, and M. Veldhorst, Operating semiconductor quantum processors with hopping spins, Science 385, 447 (2024).
  12. A. M. J. Zwerver et al., Qubits made by advanced semiconductor manufacturing, Nat. Electron. 5, 184 (2022).
  13. S. Neyens et al., Probing single electrons across 300-mm spin qubit wafers, Nature (London) 629, 80 (2024).
  14. P. Steinacker et al., A 300 mm foundry silicon spin qubit unit cell exceeding 99% fidelity in all operations, arXiv:2410.15590.
  15. I. Bloch, J. Dalibard, and S. Nascimbène, Quantum simulations with ultracold quantum gases, Nat. Phys. 8, 267 (2012).
  16. P. Scholl, M. Schuler, H. J. Williams, A. A. Eberharter, D. Barredo, K.-N. Schymik, V. Lienhard, L.-P. Henry, T. C. Lang, T. Lahaye, A. M. Läuchli, and A. Browaeys, Quantum simulation of 2D antiferromagnets with hundreds of Rydberg atoms, Nature (London) 595, 233 (2021).
  17. A. H. Karamlou, I. T. Rosen, S. E. Muschinske, C. N. Barrett, A. Di Paolo, L. Ding, P. M. Harrington, M. Hays, R. Das, D. K. Kim, B. M. Niedzielski, M. Schuldt, K. Serniak, M. E. Schwartz, J. L. Yoder, S. Gustavsson, Y. Yanay, J. A. Grover, and W. D. Oliver, Probing entanglement in a 2D hard-core Bose-Hubbard lattice, Nature (London) 629, 561 (2024).
  18. M. Lodari, A. Tosato, D. Sabbagh, M. A. Schubert, G. Capellini, A. Sammak, M. Veldhorst, and G. Scappucci, Light effective hole mass in undoped Ge/SiGe quantum wells, Phys. Rev. B 100, 041304(R) (2019).
  19. N. W. Hendrickx, D. P. Franke, A. Sammak, M. Kouwenhoven, D. Sabbagh, L. Yeoh, R. Li, M. L. V. Tagliaferri, M. Virgilio, G. Capellini, G. Scappucci, and M. Veldhorst, Gate-controlled quantum dots and superconductivity in planar germanium, Nat. Commun. 9, 2835 (2018).
  20. F. van Riggelen, N. W. Hendrickx, W. I. L. Lawrie, M. Russ, A. Sammak, G. Scappucci, and M. Veldhorst, A two-dimensional array of single-hole quantum dots, Appl. Phys. Lett. 118, 044002 (2021).
  21. F. Borsoi, N. W. Hendrickx, V. John, M. Meyer, S. Motz, F. van Riggelen, A. Sammak, S. L. de Snoo, G. Scappucci, and M. Veldhorst, Shared control of a 16 semiconductor quantum dot crossbar array, Nat. Nanotechnol. 19, 21 (2024).
  22. K. Takeda, A. Noiri, T. Nakajima, L. C. Camenzind, T. Kobayashi, A. Sammak, G. Scappucci, and S. Tarucha, Rapid single-shot parity spin readout in a silicon double quantum dot with fidelity exceeding 99%, npj Quantum Inf. 10, 1 (2024).
  23. G. Burkard, T. D. Ladd, A. Pan, J. M. Nichol, and J. R. Petta, Semiconductor spin qubits, Rev. Mod. Phys. 95, 025003 (2023).
  24. J. R. Petta, A. C. Johnson, J. M. Taylor, E. A. Laird, A. Yacoby, M. D. Lukin, C. M. Marcus, M. P. Hanson, and A. C. Gossard, Coherent manipulation of coupled electron spins in semiconductor quantum dots, Science 309, 2180 (2005).
  25. M. Veldhorst, C. H. Yang, J. C. C. Hwang, W. Huang, J. P. Dehollain, J. T. Muhonen, S. Simmons, A. Laucht, F. E. Hudson, K. M. Itoh, A. Morello, and A. S. Dzurak, A two-qubit logic gate in silicon, Nature (London) 526, 410 (2015).
  26. T. F. Watson, S. G. J. Philips, E. Kawakami, D. R. Ward, P. Scarlino, M. Veldhorst, D. E. Savage, M. G. Lagally, M. Friesen, S. N. Coppersmith, M. A. Eriksson, and L. M. K. Vandersypen, A programmable two-qubit quantum processor in silicon, Nature (London) 555, 633 (2018).
  27. O. E. Dial, M. D. Shulman, S. P. Harvey, H. Bluhm, V. Umansky, and A. Yacoby, Charge noise spectroscopy using coherent exchange oscillations in a singlet-triplet qubit, Phys. Rev. Lett. 110, 146804 (2013).
  28. See Supplemental Material at http://link.aps.org/supplemental/10.1103/xhq3-4jxz, which includes Refs. [29–34], for additional details about the device and numerical simulations as well as further analysis of experimental data. Sections (I) for details about the simulation, (II) for details on the device and fabrication, (III) for experimental data where EDSR spectroscopy is used to further study the exchange interaction, (IV) for data on the quantum dot pair QD1 and QD4, (V) for analysis on the quality of the exchange oscillations.
  29. V. John, F. Borsoi, Z. György, C.-A. Wang, G. Széchenyi, F. van Riggelen-Doelman, W. I. L. Lawrie, N. W. Hendrickx, A. Sammak, G. Scappucci, A. Pályi, and M. Veldhorst, Bichromatic Rabi control of semiconductor qubits, Phys. Rev. Lett. 132, 067001 (2024).
  30. D. Stepanenko, M. Rudner, B. I. Halperin, and D. Loss, Singlet-triplet splitting in double quantum dots due to spin-orbit and hyperfine interactions, Phys. Rev. B 85, 075416 (2012).
  31. D. Jirovec, A. Hofmann, A. Ballabio, P. M. Mutter, G. Tavani, M. Botifoll, A. Crippa, J. Kukucka, O. Sagi, F. Martins, J. Saez-Mollejo, I. Prieto, M. Borovkov, J. Arbiol, D. Chrastina, G. Isella, and G. Katsaros, A singlet-triplet hole spin qubit in planar Ge, Nat. Mater. 20, 1106 (2021).
  32. J. Saez-Mollejo, D. Jirovec, Y. Schell, J. Kukucka, S. Calcaterra, D. Chrastina, G. Isella, M. Rimbach-Russ, S. Bosco, and G. Katsaros, Exchange anisotropies in microwave-driven singlet-triplet qubits, Nat. Commun. 16, 3862 (2025).
  33. M. T. Mądzik et al., Operating two exchange-only qubits in parallel, arXiv:2504.01191.
  34. P. Stano and D. Loss, Review of performance metrics of spin qubits in gated semiconducting nanostructures, Nat. Rev. Phys. 4, 672 (2022).
  35. M. D. Reed, B. M. Maune, R. W. Andrews, M. G. Borselli, K. Eng, M. P. Jura, A. A. Kiselev, T. D. Ladd, S. T. Merkel, I. Milosavljevic, E. J. Pritchett, M. T. Rakher, R. S. Ross, A. E. Schmitz, A. Smith, J. A. Wright, M. F. Gyure, and A. T. Hunter, Reduced sensitivity to charge noise in semiconductor spin qubits via symmetric operation, Phys. Rev. Lett. 116, 110402 (2016).
  36. N. W. Hendrickx, L. Massai, M. Mergenthaler, F. J. Schupp, S. Paredes, S. W. Bedell, G. Salis, and A. Fuhrer, Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity, Nat. Mater. 23, 920 (2024).
  37. L. E. A. Stehouwer, C. X. Yu, B. van Straaten, A. Tosato, V. John, D. Degli Esposti, A. Elsayed, D. Costa, S. D. Oosterhout, N. W. Hendrickx, M. Veldhorst, F. Borsoi, and G. Scappucci, Exploiting strained epitaxial germanium for scaling low-noise spin qubits at the micrometre scale, Nat. Mater. (2025), 10.1038/s41563-025-02276-w.
  38. F. Martins, F. K. Malinowski, P. D. Nissen, E. Barnes, S. Fallahi, G. C. Gardner, M. J. Manfra, C. M. Marcus, and F. Kuemmeth, Noise Suppression using symmetric exchange gates in spin qubits, Phys. Rev. Lett. 116, 116801 (2016).
  39. QTCAD/Assisted Design for Quantum Technologies | Nanoacademic, https://nanoacademic.com/solutions/qtcad/.
  40. M. Lodari, N. W. Hendrickx, W. I. L. Lawrie, T.-K. Hsiao, L. M. K. Vandersypen, A. Sammak, M. Veldhorst, and G. Scappucci, Low percolation density and charge noise with holes in germanium, Mater. Quantum Technol. 1, 011002 (2021).
  41. T. Hensgens, T. Fujita, L. Janssen, X. Li, C. J. Van Diepen, C. Reichl, W. Wegscheider, S. Das Sarma, and L. M. K. Vandersypen, Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array, Nature (London) 548, 70 (2017).
  42. H. G. J. Eenink, L. Petit, W. I. L. Lawrie, J. S. Clarke, L. M. K. Vandersypen, and M. Veldhorst, Tunable coupling and isolation of single electrons in silicon metal-oxide-semiconductor quantum dots, Nano Lett. 19, 8653 (2019).
  43. T. Tanttu et al., Assessment of the errors of high-fidelity two-qubit gates in silicon quantum dots, Nat. Phys. 20, 1804 (2024).
  44. B. Bertrand, H. Flentje, S. Takada, M. Yamamoto, S. Tarucha, A. Ludwig, A. D. Wieck, C. Bäuerle, and T. Meunier, Quantum manipulation of two-electron spin states in isolated double quantum dots, Phys. Rev. Lett. 115, 096801 (2015).
  45. M. Russ, D. M. Zajac, A. J. Sigillito, F. Borjans, J. M. Taylor, J. R. Petta, and G. Burkard, High-fidelity quantum gates in Si/SiGe double quantum dots, Phys. Rev. B 97, 085421 (2018).
  46. N. Wang, S.-M. Wang, R.-Z. Zhang, J.-M. Kang, W.-L. Lu, H.-O. Li, G. Cao, B.-C. Wang, and G.-P. Guo, Pursuing high-fidelity control of spin qubits in natural Si/SiGe quantum dot, Appl. Phys. Lett. 125, 204002 (2024).
  47. A. J. Weinstein et al., Universal logic with encoded spin qubits in silicon, Nature (London) 615, 817 (2023).
  48. M. Rimbach-Russ, S. G. J. Philips, X. Xue, and L. M. K. Vandersypen, Simple framework for systematic high-fidelity gate operations, Quantum Sci. Technol. 8, 045025 (2023).
  49. M. Nurizzo, B. Jadot, P.-A. Mortemousque, V. Thiney, E. Chanrion, D. Niegemann, M. Dartiailh, A. Ludwig, A. D. Wieck, C. Bäuerle, M. Urdampilleta, and T. Meunier, Complete readout of two-electron spin states in a double quantum dot, PRX Quantum 4, 010329 (2023).
  50. I. Seidler, T. Struck, R. Xue, N. Focke, S. Trellenkamp, H. Bluhm, and L. R. Schreiber, Conveyor-mode single-electron shuttling in Si/SiGe for a scalable quantum computing architecture, npj Quantum Inf. 8, 1 (2022).
  51. A. M. J. Zwerver, S. V. Amitonov, S. L. De Snoo, M. T. Mądzik, M. Rimbach-Russ, A. Sammak, G. Scappucci, and L. M. K. Vandersypen, Shuttling an electron spin through a silicon quantum dot array, PRX Quantum 4, 030303 (2023).
  52. M. Künne, A. Willmes, M. Oberländer, C. Gorjaew, J. D. Teske, H. Bhardwaj, M. Beer, E. Kammerloher, R. Otten, I. Seidler, R. Xue, L. R. Schreiber, and H. Bluhm, The SpinBus architecture for scaling spin qubits with electron shuttling, Nat. Commun. 15, 4977 (2024).
  53. F. van Riggelen-Doelman, C.-A. Wang, S. L. de Snoo, W. I. L. Lawrie, N. W. Hendrickx, M. Rimbach-Russ, A. Sammak, G. Scappucci, C. Déprez, and M. Veldhorst, Coherent spin qubit shuttling through germanium quantum dots, Nat. Commun. 15, 5716 (2024).
  54. S. Bravyi, A. W. Cross, J. M. Gambetta, D. Maslov, P. Rall, and T. J. Yoder, High-threshold and low-overhead fault-tolerant quantum memory, Nature (London) 627, 778 (2024).
  55. F. K. Unseld, B. Undseth, E. Raymenants, Y. Matsumoto, S. L. de Snoo, S. Karwal, O. Pietx-Casas, A. S. Ivlev, M. Meyer, A. Sammak, M. Veldhorst, G. Scappucci, and L. M. K. Vandersypen, Baseband control of single-electron silicon spin qubits in two dimensions, Nat. Commun. 16, 5605 (2025).
  56. V. John, C. X. Yu, B. van Straaten, E. A. Rodríguez-Mena, M. Rodríguez, S. Oosterhout, L. E. A. Stehouwer, G. Scappucci, S. Bosco, M. Rimbach-Russ, Y.-M. Niquet, F. Borsoi, and M. Veldhorst, A two-dimensional 10-qubit array in germanium with robust and localised qubit control, arXiv:2412.16044.
  57. C. J. van Diepen, T.-K. Hsiao, U. Mukhopadhyay, C. Reichl, W. Wegscheider, and L. M. K. Vandersypen, Quantum simulation of antiferromagnetic Heisenberg chain with gate-defined quantum dots, Phys. Rev. X 11, 041025 (2021).
  58. C.-A. Wang, C. Déprez, H. Tidjani, W. I. L. Lawrie, N. W. Hendrickx, A. Sammak, G. Scappucci, and M. Veldhorst, Probing resonating valence bonds on a programmable germanium quantum simulator, npj Quantum Inf. 9, 1 (2023).
  59. E. G. Kelly, L. Massai, B. Hetényi, M. Pita-Vidal, A. Orekhov, C. Carlsson, I. Seidler, K. Tsoukalas, L. Sommer, M. Aldeghi, S. W. Bedell, S. Paredes, F. J. Schupp, M. Mergenthaler, A. Fuhrer, G. Salis, and P. Harvey-Collard, Identifying and mitigating errors in hole spin qubit readout, arXiv:2504.06898.
  60. A. Ivlev et al., Scripts and Data for: “Operating semiconductor qubits without individual barrier gates”, Zenodo (2025), 10.5281/zenodo.15829323.

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Phys. Rev. X 15, 031042– Published 14 August, 2025
  • Received 7 January 2025
  • Revised 22 May 2025
  • Accepted 24 June 2025
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