Distinguishing co-spectral quantum graphs by scattering

We propose a simple method for resolution of co-spectrality of Schrödinger operators on metric graphs. Our approach consists of attaching a lead to them and comparing the $S$-functions of the corresponding scattering problems on these (non-compact) graphs. We show that in several cases – including general graphs on at most 6 vertices, general trees on at most 9 vertices, and general fuzzy balls – eigenvalues and scattering data are together sufficient to distinguish co-spectral metric graphs.