Scaling of subgap excitations in a superconductor-semiconductor nanowire quantum dot

The subgap excitations known as Andreev levels govern the low-energy physics of hybrid superconductor-semiconductor nanostructures, and lie at the origin of topological superconductivity. A quantitative understanding of their scaling with respect to relevant parameters is, however, still limited. Here, the authors address this issue for the prototypical case of a quantum dot coupled to a superconductor. Experimentally, the authors demonstrate the ability to controllably tune the hybridization of the dot and the superconductor. In addition, they develop a methodology to reliably extract the relevant parameters by numerically adjusting the Anderson model to the experimental data. As a result, they carefully study the scaling of Andreev levels within the parameter space and obtain an experimental phase diagram of the system. Their results show an impressive quantitative agreement with the theory.