Coherence And Two-photon Transition Of One Four-level System

The study on the dynamical properties brought about by the interaction between the light field and material has attracted the attention of researchers for its importance. The researchers pay much attention to the generalization and analysis of Jaynes-Cumming model, particularly the coherence introduced by the dynamics and the diffraction in experiments are studied. Also the application of QED systems in quantum information processing is discussed widely. We must point out that the study on the coherence of one three-level or four-level system is conducted in both the theory and experiments. It should be mentioned that the similar schemes and methods could generalized to the quantum dot systems. In the thesis, the dynamical properties of one given four-level system will be discussed theoretically.By using the full quantum mechanical theory, the coherence and two-photon transition of one four-level system are analyzed. The detailed evolution is discussed. Firstly, the effective Hamiltonian is given by using the Fr?hlich transformation. And then the coherence properties are discussed as some appropriate condition is adopted. Finally, the two-photon transition is studied using the research method of spontaneous emission in quantum electrodynamics. As the coupling coefficients are adopted same the Hamiltonian is seen to commute with the particle number operator of the light field. At the specific frequency condition, the derivation on the coherent properties is given. The analysis results show that the two levels originally non-correlated will be interacting with each other. As there is no such adoption, the two-photon transition could be seen.