工程化量子链路：城域光纤网络上的噪声与量子态退化度量
Engineering Quantum Links: Noise and Quantum-State-Degradation Metrics over Metropolitan Fiber Network
- University of Naples Federico II（那不勒斯费德里科二世大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文在7.3公里城域光纤环路上，通过实验测量建立量子链路的噪声（信噪比模拟）和误码（各自由度退化）度量，将量子组网转化为工程设计问题，为量子互联网提供链路预算要素。
AI中文摘要：
在现有网络基础设施上部署量子网络，需要与支撑经典通信相同的工程基础：对信道噪声及其对传输信息所造成损害的定量模型。在本工作中，我们基于实验测量构建了这样的基础，将经典链路表征的两个基石度量——即信噪比（SINR）和误码率（BER）——的量子网络对应物，落地于一条7.3公里长的城域光纤环路，该环路连接了那不勒斯费德里科二世大学的两个校区，并位于国家这个http URL测试平台内。在噪声方面，我们采用光子计数的信噪比量子模拟——其中暗计数构成固有噪声，而经典流量产生的光子（通过自发拉曼散射或光纤间串扰）构成干扰——并直接在部署的环路上量化每种贡献。在误码方面，我们考虑了在光学光子内编码量子态可用的主要自由度——即偏振、时间和频率——并量化每个自由度上信道引起的退化及其随时间的漂移。这些结果表明，量子光纤链路与其经典对应物一样，可以通过一小组可测量参数来刻画，从而将已部署光纤上的量子组网从物理演示转变为工程设计问题。综合起来，它们为量子互联网提供了量子链路预算的关键要素。
英文摘要：
Deploying quantum networks over existing network infrastructures requires the same engineering foundations that underpin classical communications: quantitative models of the channel's noise and of the impairments it imposes on the transmitted information. In this work, we build such a foundation on experimental measurements, grounding the quantum-network counterparts of the two cornerstone metrics of classical link characterization - namely, the SINR and the BER - on a 7.3 km deployed metropolitan-scale fiber-loop interconnecting two campuses of the University of Naples Federico II within the national QuantumInternet.it testbed. On the noise side, we adopt a photon-counting quantum analog of the SINR - in which dark counts constitute the intrinsic noise and the photons generated by classical traffic (through either spontaneous Raman scattering or inter-fiber crosstalk) constitute the interference - and we quantify each contribution directly on the deployed loop. On the bit-error side, we consider the main degrees-of-freedom available to encode a quantum state within an optical photon - namely, polarization, time, and frequency - and we quantify for each degree the channel-induced degradation and its drift over time. These results show that a quantum fiber link, like its classical counterpart, can be captured by a small set of measurable parameters, turning quantum networking over deployed fiber from a physics demonstration into an engineering design problem. Together, they provide the key ingredients of a quantum link budget for the Quantum Internet.
