Kwiat P G, Barraza-Lopez S, Stefanov A, Gisin N
Physics Division, Los Alamos National Laboratory, New Mexico 87545, USA.
Nature. 2001 Feb 22;409(6823):1014-7. doi: 10.1038/35059017.
Entangled states are central to quantum information processing, including quantum teleportation, efficient quantum computation and quantum cryptography. In general, these applications work best with pure, maximally entangled quantum states. However, owing to dissipation and decoherence, practically available states are likely to be non-maximally entangled, partially mixed (that is, not pure), or both. To counter this problem, various schemes of entanglement distillation, state purification and concentration have been proposed. Here we demonstrate experimentally the distillation of maximally entangled states from non-maximally entangled inputs. Using partial polarizers, we perform a filtering process to maximize the entanglement of pure polarization-entangled photon pairs generated by spontaneous parametric down-conversion. We have also applied our methods to initial states that are partially mixed. After filtering, the distilled states demonstrate certain non-local correlations, as evidenced by their violation of a form of Bell's inequality. Because the initial states do not have this property, they can be said to possess 'hidden' non-locality.
纠缠态是量子信息处理的核心，包括量子隐形传态、高效量子计算和量子密码学。一般来说，这些应用在纯的、最大纠缠量子态下效果最佳。然而，由于耗散和退相干，实际可用的态很可能是非最大纠缠、部分混合（即不纯）的，或者两者皆是。为了解决这个问题，人们提出了各种纠缠蒸馏、态纯化和浓缩方案。在此，我们通过实验证明了从非最大纠缠输入中蒸馏出最大纠缠态。利用部分偏振器，我们执行一个滤波过程，以最大化由自发参量下转换产生的纯偏振纠缠光子对的纠缠度。我们还将我们的方法应用于部分混合的初始态。滤波后，蒸馏态表现出一定的非局域相关性，这通过它们对一种形式的贝尔不等式的违背得以证明。由于初始态不具备这种性质，所以可以说它们拥有“隐藏”的非局域性。
