离散信号量子照明的单次探测极限
One-Shot Detection Limits of Quantum Illumination with Discrete Signals
摘要：
探测隐形目标存在的一种微创方法是用单光子探测并分析反射信号。这种传统的检测方案的效率可以通过量子照明的方法来提高，其中利用纠缠来打破经典极限。问题是，什么是最佳的量子态，使我们能够以最小的误差达到检测极限？在这里，我们解决这个问题的离散信号，推导出一个完整的和一般的一组分析解决方案，为整个参数空间，它可以分为三个不同的区域，在传统的和量子照明的相图的形式。有趣的是，当目标的反射率小于某个临界值时，所有接收到的信号都变得无用，即使使用纠缠资源也是如此。然而，确实存在量子照明可以提供优于传统照明的优势的区域;在那里，最佳信号状态是具有与环境状态的光谱成反比的纠缠光谱的纠缠状态。这些结果不仅在量子雷达等应用中施加了基本限制，而且还表明了如何对微创检测的攻击免疫。
英文摘要：
A minimally-invasive way to detect the presence of a stealth target is to probe it with a single photon and analyze the reflected signals. The efficiency of such a conventional detection scheme can potentially be enhanced by the method of quantum illumination, where entanglement is exploited to break the classical limits. The question is, what is the optimal quantum state that allows us to achieve the detection limit with a minimal error? Here we address this question for discrete signals, by deriving a complete and general set of analytic solutions for the whole parameter space, which can be classified into three distinct regions, in the form of phase diagrams for both conventional and quantum illumination. Interestingly, whenever the reflectivity of the target is less than some critical values, all received signals become useless, which is true even if entangled resources are employed. However, there does exist a region where quantum illumination can provide advantages over conventional illumination; there, the optimal signal state is an entangled state with an entanglement spectrum inversely proportional to the spectrum of the environmental state. These results not only impose fundamental limits in applications such as quantum radars, but also suggest how to become immune against the attack of minimally-invasive detection.
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