Superposition and entanglement, the quintessential characteristics of quantum physics, have been shown to provide communication, computation, and sensing capabilities that go beyond what classical physics will permit. It is natural, therefore, to explore their application to radar, despite the fact that decoherence---caused by the loss and noise encountered in radar sensing---destroys these fragile quantum properties. This paper tells the story of "quantum illumination", an entanglement-based approach to quantum radar, from its inception to its current understanding. Remarkably, despite loss and noise that destroy its initial entanglement, quantum illumination does offer a target-detection performance improvement over a classical radar of the same transmitted energy. A realistic assessment of that improvement's utility, however, shows that its value is severely limited. Nevertheless, the fact that entanglement can be of value on an entanglement-breaking channel---the meta-lesson of the quantum illumination story---should spur continued research on quantum radar.

中文翻译：

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量子照明的故事

叠加和纠缠是量子物理学的典型特征，已被证明可以提供超越经典物理学所允许的通信、计算和传感能力。因此，探索它们在雷达中的应用是很自然的，尽管退相干——由雷达传感中遇到的损耗和噪声引起——破坏了这些脆弱的量子特性。本文讲述了“量子照明”（一种基于纠缠的量子雷达方法）的故事，从诞生到目前的理解。值得注意的是，尽管损耗和噪声会破坏其初始纠缠，但与具有相同传输能量的经典雷达相比，量子照明确实提供了目标检测性能的改进。然而，对该改进效用的现实评估，表明其价值受到严重限制。然而，纠缠在打破纠缠的通道上有价值——量子照明故事的元课——这一事实应该会刺激对量子雷达的持续研究。