Entangled State Preparation Based On The Cross Kerr Nonlinearity And Researcn On Fidelity

Quantum information science is a cross discipline which arose in the eighty's of last century, which is a set of quantum theory and information theory. Mainly includes quantum communication, quantum information theory, quantum computation and quantum measurement and so on. Among them, the quantum communication has been widely concerned because of its high efficiency and security, which can not be compared with classical communication. It has become a hot research topic in the international research of quantum physics and information science. Quantum entanglement is the basis of quantum entanglement. So the preparation of entangled states is particularly important for the development of quantum communication. Fidelity is one of the important data to measure the quality of quantum communication, so how to improve the fidelity is also a key point of our research.In this paper, we mainly study the preparation of quantum entangled states and the fidelity of teleportation. This thesis consists of four parts:In chapter one: Introduces some basic concepts of quantum information science, quantum entanglement theory, theory of fidelity and decoherence theory.In chapter two: An optical scheme for the preparation of entangled coherent states is proposed, based on the cross Kerr nonlinear effect. The preparation methods of entangled coherent states and high dimensional multimode coherent states are presented. High dimensional entangled coherent states has great significance for long distance quantum communication.In chapter three: Put forward a new scheme for preparing the three photon GHZ state and GHZ state of multi photon, based on weak cross Kerr nonlinearity. Program will use the error rate is relatively low P homodyne measurement; the previous single photon interaction replacement for two-photon interaction and reduce the back effects of coherence; The device is only ues some simple basic linear optical components. Compared to the previous scheme has lower error probability and higher fidelity, and easier to achieve.In chapter four: The fidelity of the non maximally entangled coherent states is calculated by using two mode photon measurement and the odd and even measurement. It is found that the use of even and odd measurement can significantly improve the fidelity of teleportation. The design of a high fidelity, high success probability for the teleportation scheme provides reference.