Electron g-factor of valley states in realistic silicon quantum dots

TL;DR

This paper provides a theoretical model of the silicon quantum dot g-factor, revealing how interface-induced spin-orbit interactions influence spin qubit control and coherence, with implications for quantum computing.

Contribution

The paper introduces an almost fully analytic model of the silicon quantum dot g-factor considering interface symmetry and electric fields, highlighting spin-orbit effects on qubit manipulation.

Findings

g-factor depends on magnetic field direction and electric field

Identification of spin-qubit dephasing sweet spots

Electric field enables fast all-electric qubit control

Abstract

We theoretically model the spin-orbit interaction in silicon quantum dot devices, relevant for quantum computation and spintronics. Our model is based on a modified effective mass approach with spin-valley boundary conditions, derived from the interface symmetry under presence of perpendicular to the interface electric field. The g-factor renormalization in the two lowest valley states is explained by the interface-induced spin-orbit 2D (3D) interaction, favoring intervalley spin-flip tunneling over intravalley processes. We show that the quantum dot level structure makes only negligible higher order effects to the g-factor. We calculate the g-factor as a function of the magnetic field direction, which is sensitive to the interface symmetry. We identify spin-qubit dephasing sweet spots at certain directions of the magnetic field, where the g-factor renormalization is zeroed: these include perpendicular to the interface magnetic field, and also in-plain directions, the latter being defined by the interface-induced spin-orbit constants. The g-factor dependence on electric field opens the possibility for fast all-electric manipulation of an encoded, few electron spin-qubit, without the need of a nanomagnet or a nuclear spin-background. Our approach of an almost fully analytic theory allows for a deeper physical understanding of the importance of spin-orbit coupling to silicon spin qubits.