标题： 单拷贝纯化中的无条件保真度阈值及量子纠错的一些方面 显示英文标题

标题： Unconditional fidelity thresholds in single copy distillation and some aspects of quantum error correction

摘要： 噪声纠缠的蒸馏以及量子纠错中的一些相关效应被考虑。 特别是我们证明，如果只允许单向经典通信（从爱丽丝到鲍勃），并且共享的$d \otimes d$状态不是纯态，则在单份蒸馏过程中可以获得的状态最优纠缠分数$F$存在一个阈值（该值是共享状态与对称最大纠缠态之间的重叠）。 这意味着为了通过混合态进行（概率性）任意好的确定性量子隐形传态，必须发送至少一个经典比特的反向通信（从鲍勃到爱丽丝）。 在此背景下，我们提供了几种其他阈值特性，特别是对于满秩状态，最优$F$的最终阈值存在。 最后，阈值结果与纠错结果相联系。 也就是说，指出在量子计算机上使用固定数量的量子比特时，几乎任何类型的噪声只能被（概率性）纠正到某个阈值误差范围，尽管有一些（罕见）例外。 显示英文摘要

摘要： Various aspects of distillation of noisy entanglement and some associated effects in quantum error correction are considered. In particular we prove that if only one--way classical communication (from Alice to Bob) is allowed and the shared $d \otimes d$ state is not pure then there is a threshold for optimal entanglement fraction $F$ of the state (being an overlap between the shared state and symmetric maximally entangled state) which can be obtained in single copy distillation process. This implies that to get (probabilistically) arbitrary good conclusive teleportation via mixed state at least one classical bit of backward communication (for Bob to Alice) has to be sent. We provide several other threshold properties in this context including in particular the existence of ultimate threshold of optimal $F$ for states of full rank. Finally the threshold results are linked to those of error correction. Namely it is pointed out that in quantum computer working on fixed number of quantum bits almost any kind of noise can be (probabilistically) corrected only to some threshold error bar though there are some (rare) exceptions.