Experimental Preparation, Collection, Interference And Application Of Entangled Photons

It is one of the greatest achievements for mankind to develop quantum mechanics besides the theory of relativity from the beginning of the twenty century, which makes people to understand the nature of the material world more deeply. Based on many problems with obvious quantum effects in information processing, it brings out the quantum information science which is also the combination of information science and quantum mechanics. As a result, it brings the science of information into a new world. In quantum information, the information storage, said and extraction all depend on quantum state and its evolution. (Quantum state is one of the mathematical tools in quantum mechanics to describe the material world.) Obviously, quantum entangled state is one kind of the most important states, because it has wide applications in both the fields of quantum communication and quantum computation. Moreover, the research on the property of quantum entangled states give us deeper understanding on the opinion of quantum mechanics. Up to now, there have been many quantum systems which can be used to produce entanglement, such as cavity-QED, trapped ions, NMR, semiconductor materials and spontaneous parametric down-conversion (SPDC) system. The entanglement they produced include the one between atom and atom, ion and ion, charge and charge et al., while for SPDC system, it is the one between photon and photon. Because of the technical constraints, each method has its shortcomings and imperfections, in contrast, SPDC process is the most important, most often and convenient method. By virtue of the characteristic of nonlinear optical crystal, the entangled state produced in this way has high entanglement degree and high fidelity, besides, it is easy to control. All these advantages make it the most promising candidate to be applied in quantum operations. The main results of the dissertation are as follows:I. Entangled photonpairs with high brightness Currently, how to obtain entangled photon pairs with higher brightness from SPDC process has become one of the most crucial problems limiting its further implementation in both quantum communication and quantum computation. Whether for type I and type II crystals, or for phase matching and quasi-phase matching conditions, there have been many theoretical models and experimental schemes. Based on them, we try to develop the brightness to a high level, which provides essential...