Engineering Quantum Links: Noise and Quantum-State-Degradation Metrics over Metropolitan Fiber Network

• URL: http://arxiv.org/abs/2609.11359v1
• Date: Thu, 10 Sep 2026 10:45:42 GMT
• Title: Engineering Quantum Links: Noise and Quantum-State-Degradation Metrics over Metropolitan Fiber Network
• Abstract summary: We build a quantum-network counterparts of the two cornerstone metrics of classical link characterization.<n>On the noise side, we adopt a photon-counting quantum analog of the SINR.<n>On the bit-error side, we consider the main degrees-of-freedom available to encode a quantum state within an optical photon.
• Score: 4.376469285036708
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: 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.

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