  We investigate a single atom cavity-QED system directly driven by a broadband
squeezed light. We demonstrate how the squeezed radiation can be used to sense
the presence of a single atom in a cavity. This happens by transferring one of
the photons from the field in a state with even number of photons to the atom
and thereby populating odd number Fock states. Specifically, the presence of
the atom is sensed by remarkable changing in the presence of one photon and the
loss of squeezing of the cavity field. A complete study of quantum fluctuations
and the excitation of multiphoton transitions is given.
