  We consider how a single photon can probe the quantum nature of a moving
mirror in the context of quantum optomechanics. In particular, we demonstrate
how the single-photon spectrum reveals resonances that depend on how many
phonons are created as well as on the strength of the mirror-photon
interaction. A dressed-state picture is used to explain positions and relative
strengths of those resonances. The time-dependent spectrum shows how the
resonances are built up over time by the photon interacting with the moving
mirror.
