Gyongyosi Laszlo, Imre Sandor
School of Electronics and Computer Science, University of Southampton, Southampton, SO17 1BJ, UK.
Department of Networked Systems and Services, Budapest University of Technology and Economics, Budapest, H-1117, Hungary.
Sci Rep. 2020 Feb 17;10(1):2745. doi: 10.1038/s41598-020-58200-6.
Crucial problems of the quantum Internet are the derivation of stability properties of quantum repeaters and theory of entanglement rate maximization in an entangled network structure. The stability property of a quantum repeater entails that all incoming density matrices can be swapped with a target density matrix. The strong stability of a quantum repeater implies stable entanglement swapping with the boundness of stored density matrices in the quantum memory and the boundness of delays. Here, a theoretical framework of noise-scaled stability analysis and entanglement rate maximization is conceived for the quantum Internet. We define the term of entanglement swapping set that models the status of quantum memory of a quantum repeater with the stored density matrices. We determine the optimal entanglement swapping method that maximizes the entanglement rate of the quantum repeaters at the different entanglement swapping sets as function of the noise of the local memory and local operations. We prove the stability properties for non-complete entanglement swapping sets, complete entanglement swapping sets and perfect entanglement swapping sets. We prove the entanglement rates for the different entanglement swapping sets and noise levels. The results can be applied to the experimental quantum Internet.
量子互联网的关键问题在于量子中继器稳定性特性的推导以及纠缠网络结构中纠缠率最大化理论。量子中继器的稳定性特性要求所有输入的密度矩阵都能与目标密度矩阵进行交换。量子中继器的强稳定性意味着在量子存储器中存储密度矩阵有界以及延迟有界的情况下，实现稳定的纠缠交换。在此，为量子互联网构建了一个噪声尺度稳定性分析和纠缠率最大化的理论框架。我们定义了纠缠交换集这一术语，它用存储的密度矩阵对量子中继器的量子存储器状态进行建模。我们确定了最优纠缠交换方法，该方法能在不同的纠缠交换集下，根据本地存储器和本地操作的噪声，使量子中继器的纠缠率最大化。我们证明了非完全纠缠交换集、完全纠缠交换集和完美纠缠交换集的稳定性特性。我们证明了不同纠缠交换集和噪声水平下的纠缠率。这些结果可应用于实验性量子互联网。
