  We study single photon optomechanics conditioned on photon counting events.
By selecting only detection events that occur long after a photon pulse arrives
at the cavity, the optomechanical interaction time can be increased, allowing a
large momentum kick to be applied to the oscillator. We apply this to two
optomechanical cavities set up within a Mach-Zhender interferometer driven by a
single photon source. The conditional state of the mechanical modes in such a
system becomes an entangled cat state for detection times resulting in maximum
mechanical amplitude in phase space. Further we study the dynamics induced by a
second photon pulse injected into an already conditioned optomechanical cavity,
a quarter of a mechanical period after the first photon has been detected. We
illustrate how the optomechanical interaction resulting from the second photon
can be strongly suppressed allowing conditional optomechanical routing of
single photons with single photon control pulses.
