Electrical operation of hole spin qubits in planar MOS silicon quantum dots

TL;DR

This paper provides a theoretical analysis of silicon hole spin qubits in planar MOS quantum dots, focusing on electrical control, coherence, and how device parameters influence qubit performance, aiming to guide experimental optimization.

Contribution

It offers a detailed theoretical study of silicon hole quantum dots, highlighting the effects of strain, ellipticity, and magnetic field orientation on g-factors and EDSR Rabi frequencies, which is novel for this system.

Findings

In-plane g-factor is strongly affected by split-off band and strain.

Ellipticity causes significant anisotropy in g-factor, varying by 50-100%.

EDSR Rabi frequencies are comparable to germanium, with high relaxation-to-Rabi ratios.

Abstract

Silicon hole quantum dots have been the subject of considerable attention thanks to their strong spin-orbit coupling enabling electrical control. The physics of silicon holes is qualitatively different from germanium holes and requires a separate theoretical description. In this work, we theoretically study the electrical control and coherence properties of silicon hole dots with different magnetic field orientations. We discuss possible experimental configurations to optimize the electric dipole spin resonance (EDSR) Rabi time, the phonon relaxation time, and the dephasing due to random telegraph noise. Our main findings are: (i) The in-plane $g$-factor is strongly influenced by the presence of the split-off band, as well as by any shear strain. The $g$-factor is a non-monotonic function of the top gate electric field, in agreement with recent experiments. This enables coherence sweet spots at specific values of the top gate field and specific magnetic field orientations. (ii) Even a small ellipticity (aspect ratios $\sim 1.2$) causes significant anisotropy in the in-plane $g$-factor, which can vary by $50\% - 100\%$ as the magnetic field is rotated in the plane. (iii) EDSR Rabi frequencies are comparable to Ge, and the ratio between the relaxation time and the EDSR Rabi time $\sim 10^5$. For an out-of-plane magnetic field the EDSR Rabi frequency is anisotropic with respect to the orientation of the driving electric field, varying by $\approx 20\%$ as the driving field is rotated in the plane. Our work aims to stimulate experiments by providing guidelines on optimizing configurations and geometries to achieve robust, fast and long-lived hole spin qubits in silicon.