Multi-qubit Quantum Information Processing In Cavity QED

Quantum information theory is an inter-discipline of quantum mechanics and information theory, which is competent in some of impossible task within the classical information science. Quantum information theory shows the superiorities beyond compare in classical information. Quantum information theory includes quantum computation and quantum communication, quantum communication is a way of effective information transmission using quantum state as information unit, including quantum teleportation, quantum dense coding, quantum secret sharing, etc.In the study of quantum information, to implement quantum information processing means to operate the qubit, then quantum hardware is needed. The kinds of hardware for quantum information are various, and one of them is the Cavity QED. We know that there are two problems in the quantum information processing, one problem is the decoherent of quantum state, and the other is implementing the joint measurement of Bell-state. Both of the two problems are well solved in the scheme of cavity QED. Just because of this advantage, cavity QED becomes one of the most promising candidates serving as hardware of quantum information.In this paper, we will study the applications of the technology of cavity QED in quantum information. Of cause, our view is focus on the study of processing multi-qubit information. We study how to generating the multi-atom entangled state and propose some scheme to processing the quantum information on the two-atom system. The results of our study are mainly given as follows,1. Generate multi-atom entangled states via different cavity QED system,1) We propose a scheme for the generation of multi-atom entanglement via high-detuned cavity QED. This scheme can also be extended to generate the entanglement between N atoms. Because there is a large detuning between the atom and the cavity field, during the interaction within the cavity, the cavity is only virtually excited, thus there is no quantum information transfer between the atomic system and cavity field. So the requirement on the quality factor of the cavity is greatly loosened. 2) We propose another scheme for the generation of multi-atom entanglement via nonresonant cavity QED system. The distinct different from the above scheme is that we apply a classic field with certain frequency to driven the interaction between two atoms when they are sent into the cavity. By this way, we can also obtain the multi-atom entanglement. The advantage of this scheme is that there is no request of the initial states of atoms, and the whole process of the generation is very simple.2. We propose an experimentally feasible scheme for teleportation of unknown two-atom state via nonresonant cavity QED. In our scheme, the joint measurement is replaced by the single-atom measurement, because we apply a classic field with certain frequency to driven the interaction between two atoms when they are sent into the cavity. The successful probability of our scheme is 1.3. We propose a scheme for implement a special control-not (C-not) gate, which is based on the quantum teleportation. Our scheme is also based on the technology of nonresonant cavity QED, thus the joint measurement can be replaced by the single-atom measurement as we apply a classic field to driven the interaction. Because the multi-qubit gate is useful in the quantum information processing, our study is valuable.