AI 中文总结
本文针对未知回波相位的量子照明，证明采用独立同分布测量时，纠缠无法提升检测性能，非纠缠相干光已达性能极限，无量子优势。
AI 中文摘要
量子照明利用发射信号与保留闲频光之间的纠缠，可将目标检测的误差概率指数提升约4倍（6 dB），优于相同发射能量下相干态的检测性能。这一优势的前提是回波相位已知，但在实际场景中，回波相位由目标距离及其表面状态决定，难以预先获知，因此该优势在相位未知时是否仍成立尚不明确。本文将目标检测建模为复合假设检验问题，其中回波相位为所有试验共有的未知常数，且限制接收器仅能对每个副本进行独立同分布测量。我们针对任意此类测量及任意单信号模式、任意维度闲频光的输入态，在低反射率下对最坏情况误差指数进行了界定。随后证明，采用外差检测的非纠缠相干光已能在任意相位值下达到该界限，因此在该场景中纠缠无法带来优势。独立同分布测量类包含多种可实现的量子照明接收器，包括光学参量放大器和相位共轭接收器，本文结果表明，在最坏情况及反射率的一阶近似下，这些接收器均无法提供量子优势。
英文摘要
Quantum illumination exploits entanglement between a transmitted signal and a retained idler to improve the error-probability exponent of target detection by roughly a factor of four (6 dB) over that with a coherent state of the same transmitted energy. This advantage presumes a known return phase. In practice, the phase is set by the range to the target and the condition of its surface, and is difficult to know in advance. Whether the advantage survives when this phase is unknown is not obvious. Here, we cast target detection as a composite hypothesis test in which the return phase is an unknown constant common to all trials, and we restrict the receiver to independent and identical measurements on each copy. We bound the worst-case error exponent at low reflectivity for every such measurement and every input state of a single signal mode and an idler of any dimension. We then show that unentangled coherent light with heterodyne detection already saturates this bound, for every value of the phase. Entanglement therefore confers no advantage in this setting. The class of independent and identical measurements contains many implementable quantum-illumination receivers, including the optical parametric amplifier and phase-conjugate receivers. Our result shows that none of them can offer a quantum advantage in the worst case over the phase, to leading order in the reflectivity.
Comments6 pages, 1 figure
