We discuss an adiabatic cooling scheme particularly adapted to cavity QED situations, and in particular to atoms interacting with microwave cavities of exceedingly high quality factors, where it is desirable to avoid the normal damping mechanism, spontaneous emission.
Part I. We analyze how a decaying cavity field can lead to significant atomic cooling. This cooling can be intuitively understood by invoking the adiabatic theorem to characterize the dynamics of an atom dressed by a classical field. We find numerically that cooling can proceed well into the quantum regime where there are only a few photons left in the cavity, and where the adiabatic theorem ceases to be applicable. A physical interpretation of this final cooling stage is given. Part II. We evaluate a nonlinear atomic homodyne detection scheme for measuring the Wigner characteristic function of a microwave cavity field. We find numerically that the semiclassical approximation, on which this scheme is based, does not give results consistent with a full quantum calculation. We analyze the back-action of the measurements on steady-state 'macroscopic superpositions' that can be generated in high-Q microwave cavities. We show that the measurements required for a full characterization of the state destroys the macroscopic superposition such that it cannot be reconstructed by using the scheme that was used to generate it in the first place.
Dynamics of the spontaneous emission from a two-level atom embedded in a bisphere microcavity is analyzed theoretically. A bisphere supports a morphology-dependent resonance having such a high quality factor with local field enhancement that the strong coupling between the atom and the cavity can be realized. By taking full account of the photon degree of freedom, we derive theoretically the coupling constant between the atom and the cavity as well as the radiation damping constants, which are used in the conventional cavity QED approach. In addition, we show that the power spectrum of the spontaneous emission at a local observation point is strongly affected by the photon Green function.
A simple scheme is presented for generating four-photon Greenberger-Horne-Zeilinger states with a large detuned interaction between a three-level atom and two bimodal cavities. In the proposed protocol, the quantum information is encoded on Fock states of the cavity-fields, and the atomic spontaneous emission can be effectively suppressed due to the fact that the excited state of the atom is adiabatically eliminated under the large detuning condition. The detection of the atom can collapse the cavity to the desired state. The experimental feasibility of our proposal is also discussed.