Entanglement Routing in Quantum Networks: A Comprehensive Survey

TL;DR

This survey formalizes the entanglement routing problem for near-term quantum networks and surveys a broad spectrum of routing strategies that separate routing and forwarding. It introduces a modular taxonomy distinguishing proactive, reactive, virtual, and opportunistic routing, and analyzes forwarding schemes for memoryless and memory-based swapping, fidelity management, and reliability. The work evaluates algorithmic families from Dijkstra-like methods to MILP/LP formulations and AI-based approaches, and discusses protocol architectures including distributed packet switching, virtual circuit switching, and SDN-inspired control for quantum networks. It also addresses operating considerations, performance metrics, and failures, and identifies critical open questions for topology design, interoperability, evaluation, and hardware metrology. The findings support a pragmatic roadmap toward hybrid, scalable quantum networks that leverage classical-network analogies while accounting for quantum-specific constraints such as decoherence, LOCC signaling, and memory limitations.

Abstract

Entanglement routing in near-term quantum networks consists of choosing the optimal sequence of short-range entanglements to combine through swapping operations to establish end-to-end entanglement between two distant nodes. Similar to traditional routing technologies, 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 lifetime of entangled states. In this work, we formulate a practical 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 classify and discuss the studied quantum routing schemes into reactive, proactive, opportunistic, and virtual routing

Figures (20)

• Figure 1: Key quantum communication protocols for servicing end-to-end entanglement requests. Alice and Bob use quantum and classical channels to produce multiple entangled pairs with an intermediate router node. The router conducts swapping to produce the end-to-end entangled pairs, which may be further purified by Alice and Bob to meet the fidelity requirements of an application. The probabilistic nature of these protocols must be taken into account in entanglement routing strategies.
• Figure 2: Entanglement routing on a grid network topology (adapted from li2021effective). Edge $(i,j) \in \mathcal{E}$ supports multiple entangled pairs, whose capacity is denoted as $C_{ij}$. Entanglement generation between S1 (S2) and T1 (T2) is requested and one or more paths are provisioned for each request. The probabilities of successfully building an entangled pair between adjacent nodes and performing swapping are denoted as $p_{ab}$ for $(a,b) \in \mathcal{E}$ and $q_b$ for $b \in \mathcal{V}$, respectively.
• Figure 3: Taxonomy of quantum routing concepts discussed in this survey. Partial or complete entanglement distribution protocols can be built by combining approaches from identified classes.
• Figure 4: Architecture of a centralized proactive routing. The purpose of the slotted representation is only to illustrate the sequential operations involved in proactive routing.
• Figure 5: E2E entanglement distribution in distributed proactive routing. Paths can be computed by the requester, the receiver, or hop-by-hop along the path.