Forster Manuel, Winkler Severin, Wolf Stefan
Computer Science Department, ETH Zürich, CH-8092 Zürich, Switzerland.
Phys Rev Lett. 2009 Mar 27;102(12):120401. doi: 10.1103/PhysRevLett.102.120401. Epub 2009 Mar 24.
Two parts of an entangled quantum state can have a correlation, in their joint behavior under measurements, that is unexplainable by shared classical information. Such correlations are called nonlocal and have proven to be an interesting resource for information processing. Since nonlocal correlations are more useful if they are stronger, it is natural to ask whether weak nonlocality can be amplified. We give an affirmative answer by presenting the first protocol for distilling nonlocality in the framework of generalized nonsignaling theories. Our protocol works for both quantum and nonquantum correlations. This shows that in many contexts, the extent to which a single instance of a correlation can violate a Clauser-Horne-Shimony-Holt inequality is not a good measure for the usefulness of nonlocality. A more meaningful measure follows from our results.
一个纠缠量子态的两个部分在测量时的联合行为中可以存在一种关联，这种关联无法用共享的经典信息来解释。这种关联被称为非局域的，并且已被证明是信息处理中一种有趣的资源。由于更强的非局域关联更有用，自然而然会问弱非局域性是否可以被放大。我们通过提出在广义无信号理论框架下提取非局域性的首个协议给出了肯定答案。我们的协议对量子关联和非量子关联都有效。这表明在许多情况下，一个关联实例违反克劳泽 - 霍恩 - 希莫尼 - 霍尔特不等式的程度并不是衡量非局域性有用性的好方法。从我们的结果可以得出一个更有意义的衡量方法。
