| We live in the era of rapid development of information technology. Informationscience changes human life and social development greatly. Quantum informationtheory came into being in this environment. Quantum information science is anemerging discipline, which is based on the basic principles of quantum mechanics，and the relevant characteristics of the quantum system relating to computing, coding,and new information transfer. It contains the quantum entanglement, quantum secretsharing, quantum teleportation, quantum cloning and quantum key distribution. Inquantum information science, quantum key distribution has become a very importantbranch of quantum information. Its security is ensured by the quantum no-cloningtheorem and the Heisenberg uncertainty principle. Because of the extensiveapplication of quantum key distribution, it can be used as the basis of other branchesof quantum information. Based on a collective-dephasing noise of quantum keydistribution protocol, in this paper we study the special encoded logic qubits, and thenbuild that a universal quantum cloning machine to clone the selected basis vectors.In the first chapter of this thesis, we introduct some basic knowledge of quantuminformation and quantum computation, including a common quantum gates, thedensity operator, quantum key distribution and quantum decoherence.In chapter II of this paper, we describe the quantum no-cloning theorem, thecloning process,and universal quantum cloning machine for d dimensional quantumsystem. We also calculate the corresponding fidelity.In the third chapter of this paper,we first discuss a collective-dephasing noiseof quantum key distribution protocol.Through studying we find that the special logicqubits can be made by any linear combination of a three-level quantum system. Weclone the selected basis vectors by using a universal quantum cloning machine for thed dimensional quantum system and calculate the fidelity of the cloning machine. |
