Assessing the performance of quantum repeaters for all phase-insensitive Gaussian bosonic channels
Assessing the performance of quantum repeaters for all phase-insensitive Gaussian bosonic channels
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DOI：
10.1088/1367-2630/18/6/063005
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发表时间：
2016-06-03
影响因子：
3.3
通讯作者：
Wehner, S.
中科院分区：
文献类型：
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作者：
Goodenough, K.;Elkouss, D.;Wehner, S.
实验量子通信中最受欢迎的目标之一是实现量子中继器。量子中继器的性能可以通过将所获得的速率与直接传输的量子和私有容量进行比较来评估，并辅之以无限的经典双向通信。然而，这些量很难计算，从而激发了对上限的搜索。Takeoka、Guha和Wilde发现量子通道的压缩纠缠是这两种能力的上限。一般来说，仍然很难找到量子信道的压缩纠缠的确切值，但是聪明的次优压缩信道允许人们上限这个量，因此也是相应的容量。在这里，我们利用这个想法来获得任何相位不敏感的高斯玻色子通道的界限。这个界限允许人们对用于模拟跨光纤通信的大类通道的量子中继器的实现进行基准测试。特别是，我们的界限是适用于现实的情况下，有一个输入上的平均光子数的限制。此外，我们还证明了通道的压缩纠缠在通道集合中是凸的，并且我们使用了量子通道的压缩纠缠与其纠缠辅助经典容量之间的联系。在此基础上，我们得到了d维擦除通道的精确压缩纠缠和双向辅助容量，以及振幅阻尼通道和所有量子比特泡利通道的边界。特别是，我们的边界改善了以前最有名的压缩纠缠上界的去极化通道。
One of the most sought-after goals in experimental quantum communication is the implementation of a quantum repeater. The performance of quantum repeaters can be assessed by comparing the attained rate with the quantum and private capacity of direct transmission, assisted by unlimited classical two-way communication. However, these quantities are hard to compute, motivating the search for upper bounds. Takeoka, Guha and Wilde found the squashed entanglement of a quantum channel to be an upper bound on both these capacities. In general it is still hard to find the exact value of the squashed entanglement of a quantum channel, but clever sub-optimal squashing channels allow one to upper bound this quantity, and thus also the corresponding capacities. Here, we exploit this idea to obtain bounds for any phase-insensitive Gaussian bosonic channel. This bound allows one to benchmark the implementation of quantum repeaters for a large class of channels used to model communication across fibers. In particular, our bound is applicable to the realistic scenario when there is a restriction on the mean photon number on the input. Furthermore, we show that the squashed entanglement of a channel is convex in the set of channels, and we use a connection between the squashed entanglement of a quantum channel and its entanglement assisted classical capacity. Building on this connection, we obtain the exact squashed entanglement and two-way assisted capacities of the d-dimensional erasure channel and bounds on the amplitude-damping channel and all qubit Pauli channels. In particular, our bound improves on the previous best known squashed entanglement upper bound of the depolarizing channel.