Mark Friesen

Common strategies for enhancing valley splitting in Si/SiGe heterostructures include engineering sharp interfaces or growing narrow quantum wells. In this talk, I show that such strategies are often only weakly effective, and that SiGe alloy disorder is largely responsible for determining the valley splitting in many devices. Using theoretical methods and simulations, we explore effects related to diffused interfaces and specially engineered Ge concentration profiles. Comparing our results to experiments, we find that alloy disorder can quantitatively explain the wide range of valley splittings observed in nominally identical samples.  An important observation for Si qubits is that, while alloy disorder causes large spatial variations in the valley splitting, it also significantly enhances its mean value. Therefore, the ability to change a dot’s location provides a key tool for controlling the valley splitting.