Controlled Quantum Dense Coding, A Single Quantum State Transfer And Two-particle States Of Remote Preparation

Quantum information theory is a new subject as a combination of quantum mechanics and information science which mainly includes quantum computation and quantum communication. Quantum information theory has revolutionized the way in which information is processed using quantum resources such as entangled states, local operations and classical communications.Three important protocols in quantum information theory are quantum dense coding, quantum teleportation and remote state preparation. In the early time, people used EPR pairs as quantum channel. The decoherence may arise because of the interaction between quantum channel and the environment. So the entangled state used as quantum channel is always not a maximally entangled state. In this thesis, we use a non-maximally entangled state as the quantum channel.In the filed of quantum dense coding, we proposed a scheme of controlled quantum dense coding with a three-particle non-maximally Greenberger-Horne-Zeilinger(GHZ) state as quantum channel. Under the control of the third party, the controlled quantum dense coding will be performed with certain probability by introducing an auxiliary particle and proper unitary transformations.A scheme of quantum controlled teleportation of a single particle state with POVM measurement is proposed. The scheme uses a three-particle entangled W state as quantum channel, by introducing an auxiliary particle and performing a unitary trans- formation, controlled teleportation will be succeeded with certain probability.Remote state preparation is a new concept which is based on quantum teleportation theory. It is the variant of quantum teleportation in which the sender knows the quantum state to be communicated. Comparing with quantum teleportation, remote state preparation needs less classic resources and is with much simpler operation. In this paper, we proposed a scheme for remote state preparation of a two-particle state. Using a four-particle entangled state as quantum channel, teleportation will be succeeded with certain probability by introducing a set of orthogonal bases and unitary transformations.