Variability of hole spin qubits in planar Germanium

Spin qubits in SiGe epitaxial heterostructures have become a promising platform for quantum computation, showing significant advancements in scalability over the last years. This progress is partly attributed to the low levels of disorder in the vicinities of the qubits, lower than Si Metal-Oxide-Semiconductor (MOS) devices [1]. Holes in Ge/SiGe heterostructures experience a wide variety of Spin-Orbit Coupling mechanisms [2-4], which, while enabling efficient electrical spin manipulation—an important advantage for scalability with respect to their electron counterparts—can also lead to significant fluctuations in their spin properties.

In this work, we quantify with numerical simulations the variability induced by charge traps at the top SiGe/oxide defective interface of hole spin qubits in Ge [5]. We simulate a prototypical device and explore the fluctuations of their charge and spin properties. We found that while the position and size of the quantum dots remain remarkably robust to disorder, sizable fluctuations of the spin properties are expected. We discuss the implications for large-scale integrations, including crossbar architectures, the addressability of individual qubits in large qubit registers, and the exploitation of shared sweet spots to cope with the degradation of the quantum processor’s quality factors due to disorder. We finally discuss potential actions to mitigate variability, by either gate layout optimization [6] or strain engineering [7].

[1] Phys. Rev. Applied 17, 024022 (2022).

[2] Phys. Rev. B 106, 235426 (2022).

[3] Phys. Rev. Lett. 131, 097002 (2023).

[4] Phys. Rev. B 108, 205416 (2023).

[5] Manuscript in preparation.

[6] Phys. Rev. Applied 22, 024030 (2024).

[7] arXiv:2407.19854 (2024).