Influences Of Decoherence On The Generation Of A Macroscopic Superposition State And Hybrid Entangled States Using Weak Cross-Kerr Effect

Decoherence is widely accepted mechanism to explain the loss of coherence in quantum systems. Kerr medium causes a change in the refractive index and which is proportional to the intensity of the signal wave, which is called the optical Kerr effect. Currently, the influences of decoherence on the generation of a macroscopic superposition state using weak cross-Kerr effect are investigated in this thesis , and the influences of decoherence on the generation entangled states using cross-Kerr-like effect have been widely concerned.First, we have investigated that a system include a single photon and a coherent field ,and the system propagate through Kerr medium to generate a macroscopic superposition state under decoherence . Considering of the disspation of the two modes and weak Kerr nonlinear effect, we derive analytically the operator of the system in term of superoperator method. Research results show that weak cross-Kerr effect influences the degree of decoherence, and different single photon decay rates result in purity variety. We also discuss in detail that the dissipation of single photon affect the average fidelity.Second, we have discussed a two-level ion which is placed in a high-Q cavity. When interaction occurs between the ion and cavity mode, we research both free hamiltonian and interaction hamiltonian, and consider that the rotation wave approximation and the large detuning case . Furthermore , we study the influences of decoherence on the state vector in Kerr medium . It is found that hybrid entangled states preparation is prominently affected by the Kerr nonlinearity.