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arXiv quant-ph/0607108quant-ph
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四量子比特混合态与广义单态分数的隐形传态

Teleportation with a Mixed State of Four Qubits and the Generalized Singlet Fraction

Ye Yeo

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11 pages
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摘要：

最近，我们提出了一个明确的协议${\cal E}_0$，用于使用真正的四量子比特纠缠态忠实地传送任意两个量子比特态[Phys. Rev. Lett. { \bf 96}，060502（2006）]。在这里，我们表明，${\cal E}_0$与任意四量子比特混合态资源$Ξ$是等价的广义去极化双通道的概率由最大纠缠的资源组件。这些是根据我们的四量子比特纠缠态定义的。定义了广义单重态分数${\cal G}[Ξ]$，并举例说明了它的物理意义.我们认为，为了以比经典可能的更好的平均保真度传送任意两个量子比特状态，我们必须要求${\cal G}[Ξ] > 1/2$。另外，我们推测当${\cal G}[Ξ] < 1/4$时，没有纠缠可以被传送。结果表明，要确定$Ξ$对${\cal E}_0$的有用性，有必要分析${\cal G}[Ξ]$。

英文摘要：

Recently, an explicit protocol ${\cal E}_0$ for faithfully teleporting arbitrary two-qubit states using genuine four-qubit entangled states was presented by us [Phys. Rev. Lett. {\bf 96}, 060502 (2006)]. Here, we show that ${\cal E}_0$ with an arbitrary four-qubit mixed state resource $Ξ$ is equivalent to a generalized depolarizing bichannel with probabilities given by the maximally entangled components of the resource. These are defined in terms of our four-qubit entangled states. We define the generalized singlet fraction ${\cal G}[Ξ]$, and illustrate its physical significance with several examples. We argue that in order to teleport arbitrary two-qubit states with average fidelity better than is classically possible, we have to demand that ${\cal G}[Ξ] > 1/2$. In addition, we conjecture that when ${\cal G}[Ξ] < 1/4$ then no entanglement can be teleported. It is shown that to determine the usefulness of $Ξ$ for ${\cal E}_0$, it is necessary to analyze ${\cal G}[Ξ]$.

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