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中国物理B：英文版

Continuous variable entanglement swapping in a thermal environment

刘金明, 李剑, 郭光灿

Published Jun 13, 2005• 0 citations
Publisher

Abstract

With the application of a Wigner function description of a two-mode squeezed state,we study a protocol of continuous variable entanglement swapping in a noisy quantum channel.Assuming that the two initial entangled states are coupled with the same environment,we analyse the quantum state emerging from the swapping and obtain the inseparable condition for the output correlation.It is found that there is more noise resulting from the entanglement swapping than from the direct transmission,no matter what values of displacement gain are chosen.

DOI
10.1088/1009-1963/11/4/006

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With the application of a Wigner function description of a two-mode squeezed state,we study a protocol of continuous variable entanglement swapping in a noisy quantum channel.Assuming that the two initial entangled states are coupled with the same environment,we analyse the quantum state emerging from the swapping and obtain the inseparable condition for the output correlation.It is found that there is more noise resulting from the entanglement swapping than from the direct transmission,no matter what values of displacement gain are chosen.
With the application of a Wigner function description of a two-mode squeezed state, we study a protocol of continuous variable entanglement swapping in a noisy quantum channel. Assuming that the two initial entangled states are coupled with the same environment, we analyse the quantum state emerging from the swapping and obtain the inseparable condition for the output correlation. It is found that there is more noise resulting from the entanglement swapping than from the direct transmission, no matter what values of displacement gain are chosen.
Entanglement swapping of two-mode Gaussian states is investigated by use of quantum teleportation protocol of continuous variables. In the entanglement swapping protocol, we take the two-mode squeezed vacuum which is exposed in a thermal environment as a mixed-quantum-channel state and a two-mode standard form Gaussian state as an input state to be teleported. When the input state is pure, we find that the swapped state is inseparable if and only if both the input state and the quantum-channel state are entangled. When the input state is mixed and entangled, we find that the swapped state is inseparable only if the quantum-channel state is sufficiently much entangled. We also notice that the required minimum entanglement in the mixed quantum channel to maintain entanglement in the swapped state strongly depends on the global purity of the input state.
A quantum channel consisting of continuous variable quantum teleportation based on the standard protocol is investigated. It is shown that a quantum channel for continuous variable teleportation by an aribitrary entangled state is equivalent to a generalized thermalizing channel. We also study the transmission of nonclassical states by a teleportation channel with a two-mode squeezed-vacuum state in a noisy environment. The transmisson performance is evaluated by using the Glauber-Sudarshan P function and the nonclassical depth. Finally, we compare the results obtained to those of a noisy direct transmission channel. It is shown that the teleportation channel performs better than the direct transmission channel in a certain region.
We present a realistic scheme for the entanglement swapping of continuous variable, in which a two-mode squeezed vacuum state serves as a quantum channel. The position sum and momentum difference of two local modes are measured. By taking the input entangled state also as a two-mode squeezed vacuum state, we investigate the average fidelity and the von Neumann entropy of the output state. The results show that the perfect teleportation can be achieved by increasing the squeezing of the quantum channel and that any nonzero squeezing in both the quantum channel and the input entangled state is sufficient to swap the entanglement.