  Transport studies of Andreev bound states (ABSs) are complicated by the
interplay of charging effects and superconductivity. Here, we compare transport
approaches to ABS spectroscopy in a semiconductor-superconductor island to a
charge-sensing approach based on an integrated radio-frequency single-electron
transistor. Consistency of the methods demonstrates that fast, non-invasive
charge sensing allows accurate quantitative measurement of ABSs while eluding
some complexities of transport.
