  Detection of a single photon escaping an optical cavity QED system prepares a
non-classical state of the electromagnetic field. The evolution of the state
can be modified by changing the drive of the cavity. For the appropriate
feedback, the conditional state can be captured (stabilized) and then released.
This is observed by a conditional intensity measurement that shows suppression
of vacuum Rabi oscillations for the length of the feedback pulse and their
subsequent return.
