A fault-tolerant quantum blockchain deployed on commercial telecommunications network

This paper introduces a four-layer hybrid quantum blockchain architecture designed to maintain cryptographic integrity and decentralized resilience in the quantum computing era. By combining a quantum physical layer (using photonic integrated circuits) with a quantum consensus layer, the system overcomes the fundamental one-third fault-tolerance limitation inherent in classical distributed networks. The architecture was deployed over existing commercial fiber-optic infrastructure in Nanning, China, connecting five nodes in a star-like topology.

The architecture separates concerns into four layers: the application layer, the quantum consensus layer, the classical logical layer, and the quantum physical layer. The quantum physical layer utilizes a one-decoy-state BB84 protocol to generate information-theoretically secure keys. These keys support the quantum consensus layer, which employs a recursive Quantum Byzantine Agreement (QBA) protocol. This protocol uses Quantum Digital Signatures (QDS) to ensure that messages cannot be forged or repudiated, allowing the network to tolerate up to nearly 50% malicious nodes. The system's practicality was validated through a food traceability application, which managed data acquisition and ledger updates with a throughput of 500 transactions per second.

Classical blockchain networks are limited by the one-third fault-tolerance threshold, which restricts their resilience against malicious actors. Furthermore, existing classical cryptographic methods are vulnerable to future quantum computers. This work demonstrates that a hybrid approach—leveraging quantum resources for consensus and security while utilizing classical infrastructure for data transfer—is a viable, near-term solution for building secure, scalable, and fault-tolerant decentralized systems.