  We study topological phenomena of quantum walks by implementing a novel
protocol that extends the range of accessible properties to the eigenvalues of
the walk operator. To this end, we experimentally realise for the first time a
split-step quantum walk with decoupling, which allows for investigating the
effect of a bulk-boundary while realising only a single bulk configuration. We
approximate the symmetry protected edge states with high similarities and read
out the phase relative to a reference for all modes. In this way we observe
eigenvalues which are distinguished by the presence or absence of sign flips
between steps. Furthermore, the results show that investigating a bulk-boundary
with a single bulk is experimentally feasible when decoupling the walk
beforehand.
