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

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.