Studies Of Controlled Teleportation In The Presence Of Quantum Noise

A combination of quantum mechanics and information science yields a new subject, namely, quantum information science. Since the carrier of information in this subject is quantum state, all the problems related to information should be resolved by means of quantum theory. Note that quantum teleportation, originally proposed by Bennett et al in 1993, is one of the most strikingly interesting fields in quantum communication. By far, a number of studies on the teleportation of unknown quantum states by means of many entangled states as quantum channel have been proposed. Thereinto, the controlled quantum teleportation is considered to be one of the most important teleportation schemes. The feature of controlled teleportation is that the teleportation scheme between two sides depends on the assistance of the third side. In this thesis, firstly, we have a briefly review of some basic concepts of quantum information. Then we focus our research on the controlled teleportation in the presence of quantum noises. Finally, our research work is summarized and some future investigations are briefly looked ahead.We investigate controlled teleportation of a qubit via a GHZ state with the influence of phase damping in the Bloch sphere representation. We use the average trace distance to describe how close the output state is to the input state to be teleported. Our results show that the average trace distance is a function of decoherence rates and angles of the analyzer performed by the controller in the single-particle projective measurement. Moreover, for a fixed value of the decoherence rate, one can adjust the analyzer angle to achieve the optimal average trace distance.We also investigate the influence of amplitude damping at every stage of the unitary operation of controlled teleportation of a qubit by a tripartite W state in the Bloch sphere representation. We use the average fidelity to describe how much information is transferred from the initial state to the teleported state. It is shown that when a depolarized three-particle W state is used as the quantum channel, the average fidelity of teleportation is a function of the decoherence rate and the depolarizing rate. The larger the depolarizing rate is, the smaller the amplitude damping effect on the average fidelity is. Moreover, the average fidelity of teleportation with values larger than 2/3 can be obtained when the values of the decoherence rate and the depolarizing rate are chosen properly.