Time dependent processes incavity QED

University dissertation from Stockholm : Fysik

Abstract: Cavity quantum electrodynamics (QED) has become one of themost successful tools for quantum information processing, butalso for the study of other pure quantum effects. In thisthesis we investigate one such system, the micromaser; an atomtraverse a cavity and interacts with the quantized modes of thecavity field. Today, the relaxation times of the atom and thecavity field can be made orders of magnitude longer than singleinteraction times, which makes it possible to carry out severaloperations on the system before decoherence becomessignificant. One can often, to a good approximation, treat themicromaser problem by considering the atom as a two-levelsystem interacting with just one of the modes, and losses ofthe combined system can be neglected during the interaction.Any rotations of the atomic Bloch vector during the interactionare, in principle, achievable with modern laser techniques. Forexample, the atom can be Stark shifted in a controlled fashionwith external lasers while it passes through the cavity.The micromaser is theoretically well described by the famousJaynes-Cummings model. Here we look into the problem arisingwhen the parameters of the Jaynes-Cummings model, which are theatom-field coupling and detuning, are allowed to vary in time.What possibilities may occur by letting the parameters dependon time? This question is fairly unanalyzed in the literatureand we are especially interested in preparing variousnon-classical states of the field. The states of the atoms aremeasured after the interactions with thefield and we considerboth the cases when the results of the detections are collectedor not. It is shown that, both in the non-selective andselective measurement procedure, any Fock state can begenerated. We also discuss how one can heat up or cool down thefield and how to prepare entangled states including more thanone mode. The photon field statistics are investigated when theparameters becomes time dependent and field losses areconsidered.

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