Quantum Dense Coding With Quantum Entangled States

Recently, quantum information theory (QIT) has become one of frontier areas in physics and information science. It not only exhibits quite significance on deeply understanding foundations of contemporary physics(especially quantum mechanics), but also has quite fascinating potential applications to transmission and processing of information and highly precise measurement. It has revealed an unprecedently deep link between the foundations of computer science and the foundations of physics. Quantum entanglement(QE) is the basis of quantum information theory. It is QE that leads to a lot of non-classical effects which are sources of a number of future high technologies, such as quantum computation, quantum cryptography, quantum dense coding and quantum teleporation. QE is a resource in physics of quantum information, as it is a main reason for fundamental differences with classical information. In fact, one of the goals of QIT is understanding QE.This thesis is devoted to investigating characteristics of QE and one of its important applications: quantum dense coding. We not only investigate some QE measures such as partial entropy entanglement, entanglement of formation and relative entropy entanglement but also work out the entanglement of some particular entangled states. Discrete and continuous quantum variables quantum dense coding can be realized with entangled staes. We study quantum dense coding between two arbitrarily fixed particles in a (N+2)-particle maximally-entangled states through introducing an auxiliary qubit and carrying out local measurements. It is shown that the transmitted classical information amount through such an entangled quantum channel is usually less than two classical bits. However, with certain conditional measurement control paramenters the information amount may reach its maximal value two classical bits information. In this case, the transimtted information amount is independent of the number of the entangled particles in the initial entangled state. Actually, this independence of the number of the entangled particles in the initial entangled state reveals a kind of localization phenomenon of the classical information capacity in the multi-particle entangled quantum channel;this localization cannot be involved in any three- particle entangled quantum channel. The results offer deeper insights into quantum dense coding via quantum channels of multi-particl entangled states. We also generalize controlled dense coding through three-particles GHZ states to controlled dense coding through (N+2)-particles GHZ states.