Scalable Graph State Generation with O(1) Local Feedforward in Quantum Networks

2026-06-15

AI Summary

This work addresses the fundamental tension in quantum networks between the probabilistic nature of long-range entanglement generation and the limited coherence times of qubits, which causes conventional routing protocols to suffer fidelity loss due to accumulated classical communication delays. To overcome this, the authors propose a routing protocol based on local measurements and classical feedforward that achieves an amortized O(1) decision complexity for the first time, ensuring end-to-end latency well below qubit coherence times. By integrating erasure-converting codes, spatial multiplexing, and branch independence, the protocol enables efficient generation of high-fidelity star-shaped subgraphs on a dual-species trapped-ion platform. This approach significantly suppresses noise and supports scalable graph-state construction, offering a resource-efficient and temporally feasible pathway toward fault-tolerant distributed quantum computing.

Abstract

The development of quantum networks faces a key challenge: the contradiction between probabilistic long-range entanglement generation and finite coherence time. Existing routing protocols typically focus on global state computation or path optimization. As the network scales up, classical delays accumulate and exacerbate decoherence, leading to a decrease in entanglement fidelity. To reduce routing decision delays to levels far below the coherence time of qubits, we propose a protocol based on local measurement and classical feedforward. This protocol reduces the local decision complexity to amortized O(1) level, ensuring that the decision delay is always much smaller than the coherence time of qubits. We map this protocol onto a dual-species trapped-ion platform and perform hybrid simulations. The results show that the proposed protocol performs well in terms of both resource efficiency and time feasibility. Noise analysis indicates that readout fidelity is the main bottleneck of this protocol, but noise suppression can be achieved by employing an erasure transformation in the dual-species architecture, combined with spatial multiplexing and branch independence, thereby ensuring the generation of high-fidelity star subgraphs. This protocol provides a clear path to achieving high-fidelity star subgraphs. These subgraphs can serve as general modules, merging to construct arbitrary subgraphs, providing a feasible solution for future fault-tolerant distributed quantum computing.

Problem

• quantum networks
• entanglement generation
• coherence time
• routing delay
• graph state

Innovation

• local feedforward
• O(1) decision complexity
• graph state generation
• dual-species trapped ions
• erasure conversion