Preparation And Study Of Entangled States In Quantum Information

Quantum information is a new subject, which is a combination of quantum mechanics and information. Nowadays some flourish progress about quantum information has been obtained in both theory and experiment, meanwhile quantum information has shown some distinguished advantages compared with classical information. With the development of quantum information, entangled states are not only used to testify some basic quantum theories, but also used as a kind of efficient resource in quantum dense coding, quantum teleportation, and so on. It can be said that quantum entangled states are involved in almost every part of quantum information and play an important role in quantum information.What are entangled states, which distinctive qualities do entangled states have and how to prepare entangled states? In this thesis we discuss these three aspects in detail and our main research work is outlined as follows: In section 2 we first give a definition of entanglement and illustrate some distinctive qualities of entangled states, then explain how to describe entanglement of multi-particle quantum state. In section 3 we show many existing different schemes for preparation of entangled states by spontaneous parametric down conversation, cavity quantum electrodynamics and iron traps, moreover we present new schemes to prepare multi-atom entangled states as well as multi-cavity entangled states. In the last section, we show how entangled states are used in quantum dense coding, quantum cryptography and quantum teleportation. A new valuable scheme based on linear optical elements about teleportation of two-photon and multi-photon entangled states also has been proposed in this section. In this scheme the probability of the successful teleportation is 50%, which is optimal.