[论文解读] Improved detection of lossy channels by two-mode correlated probes

Carmen Invernizzi, Matteo G. A. Paris|arXiv (Cornell University)|Nov 11, 2010

Quantum Information and Cryptography参考文献 3被引用 1

一句话总结

本文研究了用于检测损耗玻色通道的最优量子态，表明在能量和压缩度固定的情况下，两模压缩真空态在损耗检测中优于单模态态，尤其在高损耗情况下表现更优。关键结果表明，通过纠缠、互信息和量子失谐等量子关联可一致提升检测性能，使得两模压缩热态在现实条件下具有普遍优越性。

ABSTRACT

We consider the discrimination of lossy bosonic channels and focus to the case when one of the values for the loss parameter is zero, i.e., we address the detection of a possible loss against the alternative hypothesis of an ideal lossless channel. This discrimination is performed by inputting one-mode or two-mode squeezed thermal states with fixed total energy. By optimizing over this class of states, we find that the optimal inputs are pure, thus corresponding to single- and two-mode squeezed vacuum states. In particular, we show that for any value of the damping rate smaller than a critical value there is a threshold on the energy that makes the two-mode squeezed vacuum state more convenient than the corresponding single-mode state, whereas for damping larger than this critical value two-mode squeezed vacua are always better. We then consider the discrimination in realistic conditions, where it is unlikely to have pure squeezing. Thus by fixing both input energy and squeezing, we show that two-mode squeezed thermal states are always better than their single- mode counterpart when all the thermal photons are directed into the dissipative channel. Besides, this result also holds approximately for unbalanced distribution of the thermal photons. Finally, we also investigate the role of correlations in the improvement of detection. For fixed input squeezing (single-mode or two-mode), we find that the reduction of the quantum Chernoff bound is a monotone function of the two-mode entanglement as well as the quantum mutual information and the quantum discord. We thus verify that employing squeezing in the form of correlations (quantum or classical) is always a resource for loss detection whenever squeezed thermal states are taken as input.

研究动机与目标

• 为了改进对损耗玻色通道的检测，特别是区分零损耗（理想）与非零损耗情况。
• 确定在总能量和压缩度固定条件下，两模关联探针是否在损耗检测中优于单模探针。
• 评估量子与经典关联在利用压缩热态提升检测性能中的作用。
• 评估现实缺陷（如非零热噪声和光子分布不平衡）的影响。

提出的方法

• 在总能量固定的单模与两模压缩热态中进行优化，以确定损耗检测的最优输入态。
• 将量子切尔诺夫界作为区分无损与有损通道性能的度量标准。
• 利用纠缠、量子互信息和量子失谐来评估量子关联，以量化其在提升检测性能中的作用。
• 在不同衰减率和能量阈值下，比较两模压缩真空态与单模压缩真空态的性能。
• 通过固定输入能量与压缩度（包括热光子分布不平衡）来评估在现实条件下的性能。
• 使用解析与数值方法计算不同参数区域下的量子切尔诺夫界与关联度量。

实验结果

研究问题

• RQ1 在总能量与压缩度固定条件下，使用两模压缩态是否能提升对损耗通道的检测性能，相比单模态？
• RQ2 在何种临界衰减率以上，两模压缩态始终优于单模态？
• RQ3 量子关联（纠缠、互信息与失谐）如何促进损耗检测性能的提升？
• RQ4 当热光子在两模间分布不均时，两模探针的性能优势是否依然存在？
• RQ5 经典关联与量子纠缠在多大程度上协同增强对玻色通道中损耗的检测？

主要发现

• 当总能量超过依赖于衰减率的阈值时，两模压缩真空态是损耗检测的最优选择。
• 在衰减率低于临界值时，仅当能量足够高时，两模探针才优于单模探针；否则单模探针更优。
• 在衰减率高于临界值时，无论能量高低，两模压缩真空态始终优于单模态。
• 当能量与压缩度均固定时，若所有热光子均注入损耗通道，两模压缩热态始终优于单模态。
• 量子切尔诺夫界的减小是两模纠缠、量子互信息与量子失谐的单调函数，表明所有形式的关联均能增强检测性能。
• 在使用压缩热态作为输入时，以量子或经典关联形式引入压缩，始终有利于损耗检测。