g-factor theory of Si/SiGe quantum dots: spin-valley and giant renormalization effects

TL;DR

This paper develops a comprehensive theory for the $g$-factor in Si/SiGe quantum dots, revealing significant renormalization and suppression effects due to spin-valley interactions, with implications for qubit design.

Contribution

The authors present a general, computable $g$-factor theory applicable to all Si/SiGe heterostructures, including novel structures like Wiggle Well, highlighting new $g$-factor control mechanisms.

Findings

Significant $g$-factor renormalization in Wiggle Well structures.

Giant $g$-factor suppression due to spin-valley coupling.

Theory applicable to current Si/SiGe heterostructures.

Abstract

Understanding the $g$-factor physics of Si/SiGe quantum dots is crucial for realizing high-quality spin qubits. While previous work has explained some aspects of $g$-factor physics in idealized geometries, the results do not extend to general cases and they miss several important features. Here, we construct a theory that gives $g$ in terms of readily computable matrix elements, and can be applied to all Si/SiGe heterostructures of current interest. As a concrete example, which currently has no $g$-factor understanding, we study the so-called Wiggle Well structure, containing Ge concentration oscillations inside the quantum well. Here we find a significant renormalization of the $g$-factor compared to conventional Si/SiGe quantum wells. We also uncover a giant $g$-factor suppression of order $\mathcal{O}(1)$, which arises due to spin-valley coupling, and occurs at locations of low valley splitting. Our work therefore opens up new avenues for $g$-factor engineering in Si/SiGe quantum dots.