Quantum target detection is an emerging application that utilizes entanglement to enhance the sensing of the presence of an object. Although several experimental demonstrations for certain situations have been reported recently, the single-shot detection limit imposed by the Helstrom limit has not been reached because of the unknown optimum measurements. Here we report an experimental demonstration of quantum target detection, also known as quantum illumination, in the single-photon limit. In our experiment, one photon of the maximally entangled photon pair is employed as the probe signal and the corresponding optimum measurement is implemented at the receiver. We explore the detection problem in different regions of the parameter space and verify that the quantum advantage exists even in a forbidden region of the conventional illumination, where all classical schemes become useless. Our results indicate that quantum illumination breaks the classical limit for up to 40%, while approaching the quantum limit imposed by the Helstrom limit. These results not only demonstrate the advantage of quantum illumination, but also manifest its valuable potential of target detection.

中文翻译：

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接近基本 Helstrom 极限的实验性量子目标检测

量子目标检测是一种新兴应用，它利用纠缠来增强对物体存在的感知。尽管最近报道了针对某些情况的一些实验演示，但由于未知的最佳测量值，尚未达到 Helstrom 限制施加的单次检测限制。在这里，我们报告了单光子极限下量子目标检测（也称为量子照明）的实验演示。在我们的实验中，最大纠缠光子对中的一个光子用作探测信号，并在接收器处实现相应的最佳测量。我们探索了参数空间不同区域的检测问题，并验证了即使在常规照明的禁区中也存在量子优势，所有经典方案都变得毫无用处。我们的结果表明，量子照明打破了经典极限高达 40%，同时接近 Helstrom 极限强加的量子极限。这些结果不仅证明了量子照明的优势，也体现了其在目标检测方面的宝贵潜力。