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