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arXiv:2609.11387

Entanglement Meets Reality: A Network Engineering Assessment and Forecast of Rackable Entanglement Sources

Laura d'Avossa, Daniela Salvoni, Angela Sara Cacciapuoti, Marcello Caleffi

quant-phSubmitted Sep 10, 2026• Announced Sep 11, 2026• 0 citations
arXivHTMLPDF

Abstract

Quantum networks are transitioning from labo- ratory experiments to real-world deployments, with entangle- ment as their fundamental resource. Since an entanglement source effectively defines a quantum network, its performance directly impacts the reliability, scalability, and efficiency of future quantum communications. In this work, we investigate rack-mountable plug-and-play entangled-photon sources from a network engineering perspective, shifting the focus from device characterization to deployment-oriented performance evaluation. Building upon an extensive experimental campaign, we assess commercially deployable hardware across multiple operating conditions, evaluate current state-of-the-art capabilities, and pro- vide an outlook on future generations of entanglement sources. We identify and evaluate two key performance indicators (KPIs): multi-photon generation, capturing deviations from ideal single- pair emission, and entanglement quality, quantified through the reconstructed two-qubit density matrix. By combining the measured detected-pair rate with the one-way hashing bound derived from each density matrix, we estimate a lower bound on the achievable distillable-entanglement generation rate, providing a compact metric that captures the trade-off between pair throughput and entanglement quality. Finally, we translate these experimental results into lower bounds on the quantum-memory coherence time required for entanglement distillation, directly linking optical source performance to the hardware requirements of future quantum repeater nodes.

Comments
This work has been funded by the European Union under Horizon Europe ERC-CoG grant QNattyNet ("Quantum-Native Communication Networks: from Quantum Message to Quantum Functioning"), n.101169850. Details at https://qnattynet.quantuminternet.it

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Quantum networks are transitioning from labo- ratory experiments to real-world deployments, with entangle- ment as their fundamental resource. Since an entanglement source effectively defines a quantum network, its performance directly impacts the reliability, scalability, and efficiency of future quantum communications. In this work, we investigate rack-mountable plug-and-play entangled-photon sources from a network engineering perspective, shifting the focus from device characterization to deployment-oriented performance evaluation. Building upon an extensive experimental campaign, we assess commercially deployable hardware across multiple operating conditions, evaluate current state-of-the-art capabilities, and pro- vide an outlook on future generations of entanglement sources. We identify and evaluate two key performance indicators (KPIs): multi-photon generation, capturing deviations from ideal single- pair emission, and entanglement quality, quantified through the reconstructed two-qubit density matrix. By combining the measured detected-pair rate with the one-way hashing bound derived from each density matrix, we estimate a lower bound on the achievable distillable-entanglement generation rate, providing a compact metric that captures the trade-off between pair throughput and entanglement quality. Finally, we translate these experimental results into lower bounds on the quantum-memory coherence time required for entanglement distillation, directly linking optical source performance to the hardware requirements of future quantum repeater nodes.
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Entangled photon pair sources are a key enabling technology for quantum communication and networking, yet their deployment beyond laboratory environments is hindered by system-level complexity, limited operational stability, and insufficient industry compatibility. Here, we demonstrate a rack-based, mobile quantum light source architecture based on a semiconductor quantum dot emitter that directly addresses these challenges through modular system integration and automated operation. The source generates polarization-entangled photon pairs with an entanglement negativity 2n of up to 0.98(1)0.98(1)0.98(1), confirming near-maximal entanglement quality. In continuous, hands-off operation over a six-hour time window, the system achieves an average single-photon emission rate of 697(8)697(8)697(8) kHz and a maximum rate of 740(7)740(7)740(7) kHz, while maintaining 2n-value of more than 959595 %\%%. These results are enabled by the integration of optical excitation, collection, cryogenic operation, and control electronics within a standardized rack footprint, together with automated monitoring. By demonstrating simultaneously high entanglement quality, sustained brightness, and long-term operational stability in an industry-aligned system architecture, this work advances semiconductor quantum dot sources toward deployable entangled photon sources for applied quantum photonics.
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A quantum entanglement source distributing entangled photons to multiple users is an indispensable component of a quantum network. Furthermore, the development of affordable and easy-to-use entanglement sources can pave the way for widespread deployment of quantum networks. Here, a cost-effective, rack-mountable, fiber-based entanglement source in the telecom band has been developed. Based on second-order nonlinear optical processes in one periodically poled lithium niobate waveguide utilizing a reflection scheme, the source exhibited good signal-to-noise characteristics at high photon pair generation rates with a broadband spectrum covering the entire C-band and parts of the S-band and L-band. Three different wavelength-correlated energy-time and time-bin entangled photon pairs were demonstrated, whose entanglement properties were verified by measuring interference fringes with visibilities exceeding 96.5% for energy-time entanglement and 91.1% for time-bin entanglement. This source has great potential for implementing practical quantum networks and other scenarios.
Quantum networks exhibit enhanced performance compared to their classical counterparts, enabling secure communication and enhanced sensing protocols. Scalable quantum networks must transmit photons over distances ranging from kilometers to metropolitan scales while preserving entanglement. The objective of this thesis is to characterize the sources and switches of real-world deployed quantum networks, which require an intimate knowledge of nonlinear concepts and devices that drive these operating regimes. Importantly, quantum networks are deployed alongside existing classical communication infrastructure to ensure scalability and compatibility with established fiber-based systems. As a result, quantum and classical signals must coexist within the same telecommunication network. Because quantum infrastructure relies on optical fiber, these networks are susceptible to instabilities arising from fiber- induced effects. To fully realize a scalable quantum network, we investigated the quantum physical layer to optimize performance and identify limitations in our networking system. We characterized the performance of an entangled-photon source used to produce polarization-entangled photons. We then observe how well a high-speed, low-loss quantum switch preserves entanglement, demonstrating its utility for transmitting photons to different nodes in scalable quantum networks. We then analyze a 30 km deployed fiber located in the DC metropolitan area to examine how fiber-induced effects influence network performance. Quantum networks uniquely leverage quantum phenomena to enable fundamentally secure communication and distributed quantum computing beyond the capabilities of classical systems. To realize these advantages, careful characterization of the quantum physical layer and deployed fiber-based networks is essential, as it ensures the stability, reliability, and high-fidelity operation required for large-scale quantum network applications.
Enabling quantum capabilities in future generations of networks requires integrating quantum hardware into existing network infrastructure and developing new protocols for quantum communications. However, the cost and inherent noise associated with quantum hardware necessitate an efficient deployment strategy with a minimal number of quantum repeaters and memories. In this paper, we introduce a comprehensive network planning framework for distributing quantum hardware across existing infrastructure, with the objective of maximizing quantum network utility within an entanglement distribution network. We showcase the results of our framework using a dumbbell network topology as a preliminary example and the SURFnet network as a real-world case study. We explore the impact of quantum memory multiplexing within quantum repeaters, as well as the influence of memory coherence time on quantum network utility. We further examine the effects of different fairness assumptions on network planning, unveiling their ramifications on real-time network performance.