Entanglement Routing Techniques for Quantum Communication Networks

Entanglement routing on quantum communication networks consists of choosing the optimal sequence of local entanglements to combine through swapping operations to establish end-to-end entanglement between a source and a destination node on a quantum network. Similar to classical network routing, a quantum routing protocol uses network information to choose the best paths to satisfy a set of end-to-end entanglement requests. However, in addition to network state information, a quantum routing protocol must also take into account the requested entanglement fidelity, the probabilistic nature of swapping operations, and the short coherence times of bi-partite entangled states when conducting path selection and path recovery. In this work, we formally define the entanglement routing problem, and analyze and categorize the main approaches to address it, drawing comparisons to and inspiration from classical network routing strategies where applicable. We draw comparisons between well-studied routing strategies, including reactive, proactive, opportunistic, and virtual routing for quantum networks. Assessment of relevant algorithms, protocol designs, and published studies provide network engineers with guidelines for efficient designs of intermediate-scale quantum networks.