AA2 – Nano and Quantum Technologies

Project

AA2-17

Coherent Transport of Semiconductor Spin-Qubits: Modeling, Simulation and Optimal Control

Project Heads

Tobias Breiten, Markus Kantner, Thomas Koprucki

Project Members

Lasse Ermoneit

Project Duration

01.04.2023 − 31.03.2026

Located at

WIAS

Description

Spin qubits in gate-defined semiconductor quantum dots (QDs) are one of the major candidates for the realization of fault-tolerant universal quantum computers. Ongoing advances in the growth of SiGe heterostructures with isotopically purified 28Si quantum wells that have zero nuclear spin have enabled exceptionally long coherence times. Moreover, the compatibility with industry standard fabrication technology opens up excellent prospects for scaling up Si/SiGe-based quantum processors to very large numbers of qubits. Recently, small-scale devices have been demonstrated, which execute one- and two-qubit logic gates as well as initialization and read-out operations with high fidelity using all-electrical control.

The wiring and interconnection of large arrays of tunnel-coupled QDs, however, is a challenging problem as numerous control signals must be routed from external sources to every QD. While control lines can be stacked in multiple layers, there are clear limitations in view of geometric constraints. A possible solution to this fan-out problem is partitioning of the qubit register into smaller QD arrays interconnected by coherent quantum links, which allow to shuttle electrons in a conveyor belt mode along a one-dimensional channel.

This project is devoted to modeling, simulation and optimal control of quantum bus devices for scalable semiconductor-based quantum processors. The key objectives of the project are:

  • Modeling of realistic material defects and alloy disorder in Si/SiGe heterostructures
  • Numerical simulation of wave packet shuttling and assessment of qubit transfer fidelity
  • Application of quantum optimal control theory for computation of transfer protocols to maximize the fidelity

 

Related Pictures

Simulation of a quantum bus (AA2-17)

External Website

https://www.wias-berlin.de/research/fps/fp2/

Related Publications

  1. L. Ermoneit, B. Schmidt, T. Koprucki, J. Fuhrmann, T. Breiten, A. Sala, N. Ciroth, R. Xue, L. R. Schreiber, and M. Kantner: Optimal control of conveyor-mode spin-qubit shuttling in a Si/SiGe quantum bus in the presence of charged defects, WIAS Preprint 3082 (2023). DOI: 10.20347/WIAS.PREPRINT.3082

  2. L. Ermoneit, A. Thayil, T. Koprucki, and M. Kantner. Exact multivalley envelope function theory of valley splitting in Si/SiGe nanostructures. Phys. Rev. B 113 (2026). DOI:10.1103/md2x-s44y.

  3. A. Thayil, L. Ermoneit, and M. Kantner. Theory of valley splitting in Si/SiGe spin-qubits: Interplay of strain, resonances and random alloy disorder. Phys. Rev. B 112, 115303 (2025). DOI:10.1103/4sdz-f9cr

  4. N. Ciroth, A. Sala, R. Xue, L. Ermoneit, T. Koprucki, M. Kantner, and L. R. Schreiber. Numerical simulation of charged-defect-induced decoherence in conveyor-mode spin qubit shuttling in Si/SiGe. arXiv.2512.03588 (2025). Accepted for publication in Phys. Rev. B.
    DOI: 10.1103/styv-ypg9
  5. A. Thayil, L. Ermoneit, L. R. Schreiber, T. Koprucki, and M. Kantner. Optimization of Si/SiGe heterostructures for large and robust valley splitting in silicon qubits. arXiv:2512.18064 (2025). DOI: 10.48550/arXiv.2512.18064.
  6. L. Ermoneit: Modeling and Simulation of Si/SiGe Qubits: Disorder, Dynamics and Optimization. Ph.D. thesis, Technical University of Berlin (2026).

  7. L. Ermoneit, B. Schmidt, J. Fuhrmann, T. Koprucki, L. R. Schreiber and M. Kantner, Simulation of Single-Electron Shuttling for Spin-Qubit Transport in a SiGe Quantum Bus, Proc. International Workshop on Computational Nanotechnology (IWCN 2023, Barcelona), pp. 88-89 (2023)

  8. M. Kantner, A. Thayil, L. Ermoneit, and T. Koprucki. Optimization of Si/SiGe heterostructures forlarge and robust valley splitting in spin qubits. Proceedings of the International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD 2026, Cork), 2026. URL: https://www.nusod.net/
    wp-content/uploads/abstracts/2026/NUSOD26_ThC01.pdf.
  9. A. Thayil, L. Ermoneit, and M. Kantner. Epitaxial profile optimization for valley splitting enhancement in Si/SiGe spin-qubits. Proceedings of the International Conference on Simulation of Semiconductor Processes and Devices (SISPAD 2025, Grenoble), pp. 1–4 (2025). DOI: 10.1109/SISPAD66650.2025.11185961