发表机构
University of Pisa; Institute for Informatics and Telematics (IIT), National Research Council (CNR); Department of Physics, University of Naples Federico II; National Institute of Optics (INO), National Research Council (CNR)（比萨大学; 意大利国家研究委员会信息与遥测研究所; 那不勒斯费德里科二世大学物理系; 意大利国家研究委员会光学国家研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究提出将DAEPP与BDCZ结合的DAHR量子中继协议，推导其端到端保真度递归关系，证明该协议可大幅减少所需的BBPSSW提纯轮次，降低量子中继的光子资源消耗。
AI 中文摘要
基于Werner态提纯（BBPSSW协议）和纠缠交换（BDCZ方案）的线性量子中继链是量子网络中纠缠分发的基础，但这类中继链工作于严格的操作可靠性阈值下，且依赖资源密集型的循环提纯轮次，每轮消耗两个纠缠对以概率性地生成一个纠缠对。文献中已提出超纠缠，其可利用偏振、空间模式等多个自由度（DOF）在单个光子对内编码独立的纠缠态，由此定义了DAEPP（自由度辅助纠缠提纯协议）。我们提议将DAEPP与BDCZ方案结合，得到名为DAHR（自由度辅助超纠缠中继器）的链协议。DAEPP步骤通过消耗一个或多个自由度来提纯某一自由度的保真度。本研究中，我们提出并分析了一种DAHR变体，其将DAEPP集成到端到端路径的每一段，并与BDCZ结合。我们推导了闭式端到端保真度递归关系，该关系将单段DAEPP嵌入BDCZ方案，并为任何采用BBPSSW提纯以匹配DAHR每段有效保真度的BDCZ基准给出了严格的资源下界。在由先前实验确定的代表性非对称工作点下，我们数值证明，匹配DAHR的单光子对性能需要2至3轮BBPSSW提纯。此外，在低于临界操作可靠性时，无论多少轮BBPSSW都无法匹配DAHR的一轮DAEPP性能。
英文摘要
Linear quantum repeater chains based on Werner-state purification (the BBPSSW protocol) and entanglement swapping (the BDCZ scheme) are fundamental to entanglement distribution in quantum networks. However, they operate under a stringent operation reliability threshold and rely on resource-intensive recurrence purification rounds, each consuming two entangled pairs to probabilistically produce one. In the literature, hyperentanglement has been proposed to exploit multiple degrees of freedom (DOF), such as polarisation and spatial modes, to encode independent entangled states within a single photon pair. This has led to the definition of DAEPP (DOF-Assisted Entanglement Purification Protocol), which we propose to integrate with the BDCZ scheme, resulting in a chain protocol that we call DAHR (DOF-Assisted Hyperentanglement Repeater). The DAEPP step distils the fidelity of a DOF by consuming other(s). In this work, we propose and analyse a DAHR variant which integrates DAEPP at every segment of an end-to-end path combined with BDCZ. We derive a closed-form end-to-end fidelity recursion that embeds single-segment DAEPP into the BDCZ scheme and give a strict resource lower bound for any BDCZ baseline utilising BBPSSW purification to match DAHR's per-segment effective fidelity. At a representative asymmetric operating point informed by prior experiment, we show numerically that matching DAHR's single-photon-pair performance requires two to three rounds of BBPSSW purification. Additionally, below a critical operation reliability, no amount of BBPSSW rounds matches DAHR's one DAEPP round performance.
Comments11 pages, 6 figures, 2 tables
