论文标题
将无漏洞的非局部相关性扩展到任意较大的距离
Extending loophole-free nonlocal correlations to arbitrarily large distances
论文作者
论文摘要
量子理论最引人注目的特征之一是,它允许远距离观察者共享抵抗局部隐藏变量(经典)解释的相关性,这是一种称为贝尔非局部性的现象。除了其基本相关性外,非局部相关性使遥远的观察者能够完成经典不可思议的信息处理和加密专长,例如无条件安全的独立于设备独立的键分配方案。但是,由于检测器的高阈值效率以及非局部相关性与实验噪声的脆弱性,因此可以在最先进的铃铛实验中实现非局部相关性的距离仍然受到严重限制。我们没有寻找阈值要求略有较低的量子策略,而是利用了无漏洞的非局部相关性的性质,这些非本地相关性在当今实验可以达到的,尽管在短距离处可以实现,以扩展它们在任意较大的距离上。具体而言,我们考虑了铃铛实验,其中除了测量设置外,在空间分离的方上随机选择其测量设备的位置。我们证明,当接近源的设备是完美的,并且证明了极端漏洞的非局部相关性时,这种相关性可以扩展到远离源的设备,并具有几乎零的检测效率和可见性。为了适应靠近来源的缺陷,我们证明了一个特定的分析权衡:靠近来源的无漏洞的非局部性越高,远离来源的阈值要求就越低。我们利用这种分析折衷与最佳量子策略配对,以估算脱离源的测量设备的关键要求,并制定一种适用于通用网络方案的多功能数值方法。
One of the most striking features of quantum theory is that it allows distant observers to share correlations that resist local hidden variable (classical) explanations, a phenomenon referred to as Bell nonlocality. Besides their foundational relevance, the nonlocal correlations enable distant observers to accomplish classically inconceivable information processing and cryptographic feats such as unconditionally secure device-independent key distribution schemes. However, the distances over which nonlocal correlations can be realized in state-of-the-art Bell experiments remain severely limited owing to the high threshold efficiencies of the detectors and the fragility of the nonlocal correlations to experimental noise. Instead of looking for quantum strategies with marginally lower threshold requirements, we exploit the properties of loophole-free nonlocal correlations, which are experimentally attainable today, albeit at short distances, to extend them over arbitrarily large distances. Specifically, we consider Bell experiments wherein the spatially separated parties randomly choose the location of their measurement devices in addition to their measurement settings. We demonstrate that when devices close to the source are perfect and witness extremal loophole-free nonlocal correlations, such correlations can be extended to devices placed arbitrarily far from the source, with almost-zero detection efficiency and visibility. To accommodate imperfections close to the source, we demonstrate a specific analytical tradeoff: the higher the loophole-free nonlocality close to the source, the lower the threshold requirements away from the source. We utilize this analytical tradeoff paired with optimal quantum strategies to estimate the critical requirements of a measurement device placed away from the source and formulate a versatile numerical method applicable to generic network scenarios.