Quantum Teleportation And Quantum Dense Coding Using Superconducting Charge Qubit In Thermal Equilibrium

Quantum information science is an emerging interdisciplinary which coversquantum mechanics, information science, quantum optics and other discilines. Inrecent years, with the great increase of the human scientific and technological level, alot of theories in quantum information science program can be achieved in the realworld, such as quantum teleportation, quantum dense coding and quantum keytransmission. Quantum bit (Qubit) is the most important unit of quantum informationwhich is the key to achieve the quantum computer. The implementations of the qubitwhich have been studied are quantum dots system, superconducting quantum circuits,ion trap system, and nuclear magnetic resonance system and so on. Among thisimplementations, superconducting quantum circuits as the representative of the solidstate qubit is regarded as the most likely to be the first to achieve large-scaledquantum computer because of its good integration and excellent scalability.This thesis studies the theoretical feasibility of using two coupledsuperconducting charge qubit as the channel of the quantum teleportation and thequantum dense coding. The first chapter provides a brief review of the developmentof the quantum mechanics and quantum information science, as well as the basiccharacteristics and the basis theory of the superconducting quantum circuits. Thesecond chapter describes the basic theory of quantum information, includingquantum entanglement, quantum teleportation and quantum dense coding. In thethird chapter we mainly investigate the effects of the temperature and Josephsonenergy on teleportation of one qubit state in both the standard and the non-standardprotocols as well as the partial teleportation of an entangled state under the standardprotocol via two identical superconducting charge qubits in thermal equilibrium asthe teleportation channel, and give the analytical expression of the average fidelity.Our results show that the teleportation of one qubit state in non-standard protocol andthe partial teleportation of entanglement in standard protocol can be almost perfect,indicating that quantum teleportation, with using superconducting charge qubits inthermal equilibrium as a quantum channel, is feasible in theory. The fourth chapterinvestigates the effects of temperature and Josephson energy on dense coding with atwo-charge-qubit system coupled via a fixed capacitor. Dense coding capacities ofthis system in two cases, either identical or different qubits, are calculatedanalytically and numerically. The results show that in the case of very lowtemperature and low Josephson energy, which is the experimental condition for highquality quantum information processing, the identical superconducting-charge-qubit system is more ideal for dense coding than the case of the different one.