Generation of four-photon polarization-entangled decoherence-free states within a network (original) (raw)

We propose an optical protocol for generating four-photon polarization-entangled decoherence-free states between two arbitrary parties under control of a number of controllers in terms of optical elements. We show that the protocol can be successfully realized with a certain probability. One of the main goals of quantum information theory is to come to understand the necessary and sufficient resources for intact transmission of quantum states. In the quantum information field, there have been recently many interesting developments [1-13] based on the theory of quantum mechanics. Entanglement plays a very important role in quantum information processing [1-13]. Many of the above proposals assume, nevertheless, that the quantum channels used to implement the tasks are noiseless entangled states. But in a realistic situation, when qubits are coupled to the environment, the fragile superpositions of quantum states are easily destroyed due to decoherence and the advantage of quantum information methods is reduced. To overcome this flaw, some specific entangled states are proposed. That is, if the qubit-environment interaction, no matter how strong, exhibits some symmetry, then the quantum states are invariant under this interaction. These states are called decoherence-free states, and were originally introduced by Kempe et al. [14]. The decoherence-free states comprised by N qubits are invariant under any identical unitary transformation on each component qubit. This property makes

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