Synchronization Control-Plane Protocol for Quantum Link Layer

TL;DR

This work tackles coordination for heralded entanglement generation in multi-node quantum networks by introducing the Eventual Synchronization Protocol (ESP), a decentralized control-plane protocol operating on the quantum link layer. ESP enables end-nodes to synchronize without a central scheduler, allowing concurrent entanglement attempts and yielding markedly lower latency growth as network size increases, as demonstrated in NetSquid simulations. Compared to the baseline Distributed Queue Protocol (DQP), ESP achieves up to a sixfold improvement in latency scaling and exhibits favorable scalability and jitter characteristics across diverse topologies and fidelity settings. The results establish a practical, scalable approach for control-plane synchronization in quantum networks and point to future work on robustness, failure modes, and potential resource reservation mechanisms.

Abstract

Heralded entanglement generation between nodes of a future quantum internet is a fundamental operation that unlocks the potential for quantum communication. In this paper, we propose a decentralized synchronization protocol that operates at the classical control-plane of the link layer, to navigate the coordination challenges of generating heralded entanglement across few-qubit quantum network nodes. Additionally, with quantum network simulations using NetSquid, we show that our protocol achieves lower entanglement request latencies than a naive distributed queue approach. We observe a sixfold reduction in average request latency growth as the number of quantum network links increases. The Eventual Synchronization Protocol (ESP) allows nodes to coordinate on heralded entanglement generation in a scalable manner within multi-peer quantum networks. To the best of our knowledge, this is the first decentralized synchronization protocol for managing heralded entanglement requests.

Figures (11)

• Figure 1: Example of an eight-node quantum network topology. Each pair of nodes generates heralded entanglement using the single-photon protocol, sending entangled qubits (photons) to the heralding station $H$ using inbound fiber-optic links. Entanglement success is probabilistic and heralded by outbound classical connections. Coordinating these entanglement requests involves an additional control plane topology.
• Figure 2: Relationship of the entanglement generation probability ($p_{\text{success}}$), minimum entanglement fidelity ($F_{\text{min}}$), and bright state population ($\alpha$). This relationship is used to model the physical layer entanglement generation process within our simulations. In this example, we obtain $p_{\text{success}}$ from a $t=120$ (seconds) simulation on $2\times2$ network topology.
• Figure 3: ESP Finite State Machine Representation
• Figure 4: Example protocol state snapshot of a nine-node (3$\times$3) quantum network topology $G_Q$. E, F, G, and H are BUSY. C and I are IDLE. B and D are in SYN_SENT. F has a queued $R_{wake}$ request for I.
• Figure 5: Network topologies used in the evaluation of ESP.