Multi-particle Quantum Teleportation With Thermal Entangled Quantum Channel

This thesis discusses the quantum teleportation with unitary variables and a non-maximally-entangled quantum channel. N non-maximally entangled particle pairs are used as quantum channel to teleport an unknown N-particle entangled GHZ state and W state via entanglement swapping.The quantum teleportation means that when one teleports the unknown quantum stateψof a particle at place A to another one at place B, enable another particle to be the quantum stateψand the original particle remains at the primary place. Due to the uncertain principal of quantum mechanics, one can't extract all information from the original quantum state exactly. Therefore, one divides all information of the original quantum state into two parts: general information and quantum information. A classical channel informs general information and quantum information is informed by quantum channel. According to these messages, one can configure all information of the original quantum state at place B.In this scheme, N non-maximally entangled particle pairs are used as quantum channel to teleport an unknown N-particle entangled GHZ and W state via entanglement swapping. In order to realize this teleportation, the sender Alice operates Bell-state measurement on particles belonging to herself. Then she informs the results to the receiver Bob through classical communication. According to the results, Bob operates corresponding transformation to reconstruct the initial state. The advantage of this scheme is that it needs only one common unitary matrix for Alice's different results, which has a more general meaning. As a special case, teleporting an unknown three-particle entangled GHZ and W state are proposed.In the experience of quantum communication, maximally entangled pure states are difficult to prepare due to the effects of environment. Therefore, a quantum channel is always represented by mixed states. The thermal equilibrium state in solid state materials is one essential mixed entangled state. In this dissertation, a two-particle entangled state can be teleported through the channel of thermal mixed states in two independent 1D Heisenberg chains. We study the effects of the non-uniform external magnetic field B and temperature T on the entanglement and fidelity. We found that the entanglement will decrease with the increasing of the temperature T. And when B1 and B 2 have different directions, the entanglement teleportation is better than the classical teleportation under low temperature. Because at that case the average fidelity is always greater than 2/3.