Tis paper demonstrates that multipartite Bell-inequality violations can be fully destroyed in a finite time in three- qubit states coupled to a general XY spin-chain with a three-site interaction environment. The Mermin Ardehali- Belinksii-Klyshko inequality is used to detect the degree of nonlocality, as measured by the extent of their violations. The effects of system-environment couplings, the size of degrees of freedom of the environment and the strength of the three-site interaction on the Bell-inequality violations are given. The results indicate that the Bell-inequality violations of the tripartite states will be completely destroyed by decoherence under certain conditions for the GHZ state. The decoherence-free subspaces of our model are identified and the entanglement of quantum states is also discussed.
A simple scheme is presented for generating four-photon Greenberger-Horne-Zeilinger (GHZ) states with interaction between a four-level atom and two bimodal cavities. In the proposed protocol, the quantum information is encoded on Fock states of the cavity fields. The detection of the atom can collapse the cavity to the desired state. The experimental feasibility of our proposal is also discussed.
Feasible schemes for implementing quantum swap gates of both coherent-state qubits and photonic qubits are proposed using a A-type atomic ensemble trapped in a bimodal optical cavity. In both protocols, the decoherence from atomic spontaneous emission is negligible due to the fact that the excited states of the atoms are adiabatically eliminated under large detuning condition and the swap gates can be created in a single step. In our schemes, the required atoms-cavity interaction time decreases with the increase of the number of atoms, which is very important in view of decoherence. The experimental feasibilities of the schemes are also discussed.
A simple scheme is presented for generating four-photon entangled states with interaction between a three-level atom and two bimodal cavities.In the proposed protocol,the quantum information is encoded on Fock states of the cavity fields.The detection of the atom can collapse the cavity made/wave function to the desired state.The experimental feasibility of our proposal is also discussed.
