  We introduce the Loschmidt amplitude as a powerful tool to perform
spectroscopy of generic many-body wave functions and use it to interrogate the
wave function obtained after ramping the transverse field quantum Ising model
through its quantum critical point. Previous results are confirmed and a more
complete understanding of the population of defects and of the effects of
magnon-magnon interaction or finite-size corrections is obtained. The influence
of quantum coherence is clarified.
