Using Partially Entangled State Probability Of Dense Coding And Non-symmetrical Dense Coding Scheme

Quantum information is a new subject that is combination of information science and quantum mechanics, which includes quantum communication and computation. Quantum dense coding is an important part of quantum communication. Briefly, two parties (sender and receiver) share a pair of entangled qubits in the Bell state. The sender performs one of the four unitary operations and sends the particle to the receiver. The receiver can obtain two bits of classical information from the joint measurement on two particles. This is so called "dense coding".In practice, the entangled state used as quantum channel is always not a maximally entangled state because of interference of environment. So, in chapter III, we present two schemes for probabilistic dense coding, one is between two parties, and another is between multi-parties. They both use a non-maximally entangled state as quantum channel in essence. By introducing an auxiliary particle and performing a collective unitary operation, quantum dense coding will be succeeded with certain probability.In addition, in former schemes the quantum channels are usually symmetric, i.e., the dimension of the Hilbert space of the particle with sender is the same as that of the particle with receiver. In chapter IV, we present a scheme for dense coding in the case of non-symmetric Hilbert spaces of the sender and receiver's particles sharing the quantum maximally entangled states. The efficiency of classical information gained is also considered. We conclude that when a more level particle is with the sender, she can get a non-symmetric quantum channel from a symmetric one by entanglement transfer. Thus the efficiency of information transmission is improved.