AI 中文总结
该研究针对纠缠交换中多对发射导致虚假预示信号的问题，提出采用互补线性光学测量的级联网络，通过BSM与GM组合实现抗扰，提升了贝尔对生成的保真度与传输性能。
AI 中文摘要
多对发射是利用自发参量下转换源进行纠缠交换时虚假预示信号的主要来源。常规贝尔态测量（BSM）无法区分相邻源各发射一个光子的期望情况，与单个源发射混合偏振双光子而另一源发射真空的混合情况。我们证明，级联网络可通过让其连续交换站执行不同测量来解决这一歧义：直接基BSM可剔除同偏振双光子发射，而由四模格林机器（GM）实现的平衡赤道分析仪利用双光子干涉剔除混合偏振双光子发射，同时将BSM剔除的同偏振源间事件恢复为可分辨的φ型贝尔预示信号。这些剔除机制共同覆盖了两类单源双光子情况，同时保留了两类有用的源间事件贡献。我们对满足该条件的无源四模、可分辨光子数分析仪进行分类，确定BSM和GM为典型平衡代表。采用对多对发射所有阶次均精确的高斯态分析，我们评估了耦合、探测器及信道损耗下的三源BSM-GM和四源BSM-GM-BSM纯贝尔对源。三源网络抑制了主导非保真度，而四源网络在无损耗极限下预示出精确贝尔态，该性质适用于所有含四个及以上源的交替BSM-GM链。在所有研究的损耗水平下，其相较于源数匹配的全BSM网络的保真度优势持续存在，无需复用即可实现单通道速率优势，光谱复用将贝尔对传输概率提升至渐近确定性极限。
英文摘要
Multipair emission is a principal source of false heralds in entanglement swapping with spontaneous parametric down-conversion sources. A conventional Bell-state measurement (BSM) cannot distinguish the desired arrival of one photon from each neighboring source from a mixed-polarization double emission by one source accompanied by vacuum from the other. We show that a cascaded network can resolve this ambiguity by allowing its successive swapping stations to perform different measurements. A direct-basis BSM rejects same-polarization double emissions, whereas a balanced equatorial analyzer, implemented by a four-mode Green Machine (GM), uses two-photon interference to reject mixed-polarization double emissions. At the same time, it recovers same-polarization inter-source events rejected by the BSM as resolved $ϕ$-type Bell heralds. Their rejection sets jointly cover both single-source two-photon classes while retaining contributions from both useful inter-source classes. We classify the passive four-mode, number-resolving analyzers satisfying this condition and identify the BSM and GM as canonical balanced representatives. Using a Gaussian-state analysis exact to all orders of multipair emission, we evaluate three-source BSM--GM and four-source BSM--GM--BSM Pure Bell Pair sources under coupling, detector, and channel loss. The three-source network suppresses the leading infidelity, while the four-source network heralds an exact Bell state in the lossless limit, a property that holds for every alternating BSM--GM chain with four or more sources. The fidelity advantage over source-count-matched all-BSM networks persists at every loss level studied, a single-channel rate advantage appears without multiplexing, and spectral multiplexing raises the Bell-pair delivery probability toward the asymptotically deterministic limit.
Comments25 pages, 14 figures, 6 tables
