Study Of Quantum Communication And Quantum Cloning Theory

Quantum information science developed very quickly in recent years, it have to be one of the most impressive science development which are new in recent decades. The science of quantum information processing is promising to have a significant impact on solving algorithmic problems, how we process information, manipulate nano-scale devices and model fundamental physics.Quantum information have many wonderful effects due to it has much wonderful nature. For example, we can transmit two bits of classical information by sending only one quantum bit. This is called quantum dense coding. We also can shift the objects instantaneously and quickly. This is quantum teleportation. However, it is very challenging to make quantum information processing machines to be reality. At present, many prototype physical systems have been studied. for example, simple harmonic oscillator, cavity quantum electrodynamics, ion trap, molecule nucleus magnetic, photo and nonlinear medium, and so on.We propose a scheme for implementing quantum dense coding using four-atom cluster states in cavity QED. As one of the important concepts of quantum information, the no-cloning theorem states that the perfect copy of an unknown quantum state can not be obtained, which guarantees the absolute security of quantum cryptography. This is one of the most significant differences between classical and quantum information. Although exact cloning is impossible, one can obtain approximate copies. If quantum information could be partly cloned or could be approximately cloned to a great extent, this would seriously affect the privacy and security of quantum information when one transmits or processes it. So the research on quantum cloning has attracted much attention. We present a scheme to realize the optimal symmetric 1→2 real state quantum cloning machine in 2 dimensions with linear optical devices.The structure of our paper is as follows:Chapter 1 is the exordium. I simply introduce the quantum information knowledge, quantum entanglement and the method of preparing entanglement, the basic thought of quantum teleportation, the no-cloning theorem. In chapter 2 I introduce the preparation of entanglement and the linear optical devices. In chapter 3 I introduce the basic thought of quantum dense coding and quantum cloning. In chapter 4 I present several research results of quantum dense coding and quantum cloning. Summary and some expectations to the direction are given in chapter 5.