Group of Applied Physics, University of Geneva, CH-1211 Geneva 4, Switzerland.
Université Nice Sophia Antipolis, Laboratoire de Physique de la Matière Condensée, CNRS UMR 7336, Parc Valrose, 06108 Nice Cedex 2, France.
Phys Rev Lett. 2016 Jan 8;116(1):010401. doi: 10.1103/PhysRevLett.116.010401. Epub 2016 Jan 6.
The demonstration and use of nonlocality, as defined by Bell's theorem, rely strongly on dealing with nondetection events due to losses and detectors'inefficiencies. Otherwise, the so-called detection loophole could be exploited. The only way to avoid this is to have detection efficiencies that are above a certain threshold. We introduce the intermediate assumption of limited detection efficiency, that is, in each run of the experiment, the overall detection efficiency is lower bounded by η(min)>0. Hence, in an adversarial scenario, the adversaries have arbitrary large but not full control over the inefficiencies. We analyze the set of possible correlations that satisfy limited detection locality and show that they necessarily satisfy some linear Bell-like inequalities. We prove that quantum theory predicts the violation of one of these inequalities for all η(min)>0. Hence, nonlocality can be demonstrated with arbitrarily small limited detection efficiencies. We validate this assumption experimentally via a twin-photon implementation in which two users are provided with one photon each out of a partially entangled pair. We exploit on each side a passive switch followed by two measurement devices with fixed settings. Assuming the switches are not fully controlled by an adversary, nor by hypothetical local variables, we reveal the nonlocality of the established correlations despite a low overall detection efficiency.
贝尔定理所定义的非局域性的演示和应用强烈依赖于处理由于损耗和探测器效率低下而导致的未检测事件。否则，所谓的检测漏洞可能会被利用。避免这种情况的唯一方法是检测效率要高于某个阈值。我们引入了有限检测效率的中间假设，即在实验的每次运行中，整体检测效率都被下界限制在η（min）>0。因此，在对抗场景中，对手对效率低下的控制是任意大的，但不是完全的。我们分析了满足有限检测局域性的可能相关集，并表明它们必然满足某些线性贝尔型不等式。我们证明，对于所有η（min）>0，量子理论都预测会违反其中一个不等式。因此，即使检测效率有限，也可以演示非局域性。我们通过双光子实验进行了验证，在该实验中，两个用户从部分纠缠对中各自获得一个光子。我们在每一侧都利用一个被动开关，然后是两个具有固定设置的测量设备。假设开关不是由对手完全控制，也不是由假设的本地变量控制，我们揭示了尽管整体检测效率较低，但所建立的相关性具有非局域性。
