Centre for Quantum Technologies, National University of Singapore, Singapore 117542, Singapore.
Nat Commun. 2011 Feb 8;2:184. doi: 10.1038/ncomms1193.
The results of local measurements on some composite quantum systems cannot be reproduced classically. This impossibility, known as quantum nonlocality, represents a milestone in the foundations of quantum theory. Quantum nonlocality is also a valuable resource for information-processing tasks, for example, quantum communication, quantum key distribution, quantum state estimation or randomness extraction. Still, deciding whether a quantum state is nonlocal remains a challenging problem. Here, we introduce a novel approach to this question: we study the nonlocal properties of quantum states when distributed and measured in networks. We show, using our framework, how any one-way entanglement distillable state leads to nonlocal correlations and prove that quantum nonlocality is a non-additive resource, which can be activated. There exist states, local at the single-copy level, that become nonlocal when taking several copies of them. Our results imply that the nonlocality of quantum states strongly depends on the measurement context.
对于某些复合量子系统的局部测量结果无法在经典物理学中重现。这种被称为量子非局域性的不可能性，代表了量子理论基础的一个里程碑。量子非局域性也是信息处理任务的宝贵资源，例如量子通信、量子密钥分发、量子态估计或随机性提取。然而，确定一个量子态是否是非局域的仍然是一个具有挑战性的问题。在这里，我们引入了一种解决这个问题的新方法：我们研究了在网络中分布和测量时量子态的非局域性质。我们使用我们的框架表明，任何一种单向纠缠可提取态都会导致非局域相关，并证明了量子非局域性是一种可激活的非加性资源。存在一些在单拷贝水平上是局域的态，当取它们的多个拷贝时就会变得非局域。我们的结果表明，量子态的非局域性强烈依赖于测量环境。
