Study Of Quantum Information Processing Via W States In Cavity QED

Quantum information is an interdisciplinary subject that is a combination of quantum mechanics and information science. Compared with classical information, quantum information is much more powerful since the law of quantum mechanics is used, and thus it attracts much attention. It has two important branches: quantum computation and quantum communication. Quantum teleportation and quantum secret sharing (QSS) are the two major processes of quantum communication, and their realizations are essential for the practicality of it. At present, many physical systems have been proposed to realize quantum information processing, among which, cavity quantum electrodynamics (cavity QED) is investigated earlier and considered to be most promising one.The idea of cavity QED is to trap several atoms in a small high finesse optical cavity. Quantum information can be stored in the internal states of atoms. All the trapped atoms in cavity are coupled to the field, resulting in interaction among atoms. The decoherence effect is greatly depressed in the cavity QED.Quantum entanglement, as the communication channel, is one of the essential resources of quantum information processing. The type of entanglement affects the success probability of quantum information processing. There are only two different types of basic tripartite entangled states, i.e. GHZ-type and W-type, under stochastic local operations and classical communication (SLOCC). The W states can retain bipartite entanglement when any one of the three qubits is traced out, and thus they are much more robust than the GHZ states. So W states is consider to be better than GHZ states as quantum channel.The thesis is organized as follows: firstly, basic conceptions and resources of quantum information are introduced; several current physical systems for realizing quantum information processing is also introduced; and the essential idea and development of cavity QED are explained. Then, the theories of quantum teleportation and the W-type entangled states are reviewed; and how to teleport an unknown atomic state in cavity QED via W state is studied. Further more, the scheme for realizing QSS in cavity QED is also proposed. Our scheme is more robust against decoherence because a W-type state instead of a GHZ state is used as the quantum channel. Compared with GHZ states, n-partite W states can be obtained straightforwardly and no ancillary atoms and less cavities are required, thus our schemes are easier to implement than the schemes using GHZ states. Finally, our schemes are based on Zheng-Guo's model, thus can effectively suppress the cavity decay and are experimentally feasible with present technology.