论文标题
通过任意的许多观察者对，可回收的纠缠检测
Recycled entanglement detection by arbitrarily many sequential and independent pairs of observers
论文作者
论文摘要
我们通过顺序和独立的观察者对研究了两分点纠缠状态的见证，每对的观察者都独立于从空间分离的实验室中独立作用于他们共享状态的一部分，随后将其量子传递到顺序的下一对。以前已经猜想，不超过一对观察者可以在类似的设置中检测到clauser-horne-hold-holt“贝尔非局部”相关性。这很有趣，因为当仅允许单个观察者与另一端的多个观察者共享双分部分状态时，可能具有任意长的贝尔非局部相关性的任意序列。因此，有趣的是，当在多对观察者的情况下考虑纠缠相关性时是否也存在此类限制。我们发现，一个两倍的纠缠状态可用于通过成对的观察者任意地见证纠缠，依次和独立地行事。当序列中的初始观察者共享任何纯净的状态或从一类混合纠缠状态的类别共享一个状态时，我们证明该陈述是正确的。我们证明，对于某种类别的纠缠状态，也可以观察到这种现象，在这种状态下，在最初的纠缠含量的限制中，任意长的观察者对，见证了纠缠的极限。
We investigate the witnessing of two-qubit entangled states by sequential and independent pairs of observers, with both observers of each pair acting independently on their part of the shared state from spatially separated laboratories, and subsequently passing their qubits to the next pair in the sequence. It has previously been conjectured that not more than one pair of observers can detect Clauser-Horne-Shimony-Holt "Bell-nonlocal" correlations in a similar set-up. This is intriguing since it is possible to have an arbitrarily long sequence of Bell-nonlocal correlations when only a single observer is allowed to share a bipartite state with multiple observers at the other end. It is therefore interesting to ask whether such restrictions are also present when entangled correlations are considered in the scenario of multiple pairs of observers. We find that a two-qubit entangled state can be used to witness entanglement arbitrarily many times, by pairs of observers, acting sequentially and independently. We prove the statement to be true when the initial pair of observers in the sequence share any pure entangled state or when they share a state from a class of mixed entangled states. We demonstrate that the phenomenon can also be observed for a certain class of entangled states in which an arbitrarily long sequence of observer pairs witnessing entanglement is reached in the limit of the initial entanglement content tending to a vanishing amount.
