Detectable Byzantine Agreement (DBA) protocols abort rather than risk inconsistent decisions when verification fails. Quantum variants (QDBA) implement this detectability via multipartite entanglement checks, but in photonic networks nonuniform noise across participants makes these checks brittle: a handful of noisy nodes can trigger needless aborts or conceal adversarial behavior. We introduce two drop-in diagnosis methods that run during the standard entanglement-verification step of QDBA protocols: (i) a batch health check that detects both state leakage and insufficient fidelity, and (ii) a per-node diagnosis that estimates each participant's error rates and labels loss-biased outliers. The methods require no extra quantum rounds and add only modest classical overhead. In simulations, the batch health check substantially reduces false accepts while preserving cleanbatch acceptance, and the per-node diagnosis reliably flags noisy Lieutenants and the Commander at practical verification sizes. The techniques are compatible with existing QDBA protocols.
Detectable Byzantine Agreement (DBA) protocols abort rather than risk inconsistent decisions when verification fails. Quantum variants (QDBA) implement this detectability via multipartite entanglement checks, but in photonic networks nonuniform noise across participants makes these checks brittle: a handful of noisy nodes can trigger needless aborts or conceal adversarial behavior. We introduce two drop-in diagnosis methods that run during the standard entanglement-verification step of QDBA protocols: (i) a batch health check that detects both state leakage and insufficient fidelity, and (ii) a per-node diagnosis that estimates each participant's error rates and labels loss-biased outliers. The methods require no extra quantum rounds and add only modest classical overhead. In simulations, the batch health check substantially reduces false accepts while preserving cleanbatch acceptance, and the per-node diagnosis reliably flags noisy Lieutenants and the Commander at practical verification sizes. The techniques are compatible with existing QDBA protocols.
Quantum communication resources offer significant advantages for fault-tolerant distributed protocols, particularly in Byzantine Agreement (BA), where reliability against adversarial interference is essential. Quantum Detectable Byzantine Agreement (QDBA) enables consensus protocols that surpass classical limitations by leveraging entangled quantum states. In this work, we focus on the practical realization of QDBA using Einstein-Podolsky-Rosen (EPR) pairs, the simplest maximally entangled quantum resources, making the protocol experimentally accessible across current quantum hardware platforms. We present a comprehensive computational study of the EPRQDBA protocol under realistic quantum network conditions, utilizing the Aliro Quantum Network Simulator to evaluate the performance and robustness of the protocol. Our simulations systematically explore the protocol's parameter space --including variations in network size, traitorous node count, the amount of entanglement consumed in the protocol, and physically motivated noise models tailored specifically for superconducting and photonic qubit technologies. Through extensive numerical experiments, we provide insights into how these physically realistic parameters impact protocol performance, establishing critical thresholds and optimal operational regimes for experimental implementations. This work bridges theoretical advances in quantum consensus protocols with practical network implementations, offering a concrete reference for experimentalists. Our findings serve as a guideline for evaluating and optimizing QDBA implementations in realistic, noisy environments.
In distributed quantum computing (DQC), achieving consensus with adversarial elements presents a critical challenge. This paper proposes an innovative framework that enhances the Quantum Byzantine Agreement (QBA) protocol by integrating practical quantum error mitigation techniques, specifically Quantum Readout Error Mitigation (QREM) and Dynamical Decoupling (DD). Utilizing Noisy Intermediate-Scale Quantum (NISQ) devices, our approach aims to improve operational reliability significantly. Our results demonstrate that QREM and DD effectively mitigate common quantum channel errors through rigorous experimentation on both simulated environments and IBM’s quantum hardware. The proposed protocol also introduces a verification mechanism inspired by Quantum Key Distribution (QKD) systems, ensuring the secure transmission of commands encoded in quantum states. In cases of discrepancies, lieutenants engage in systematically designed interactions to achieve consensus, influenced by the Commander’s strategic decisions and the network’s size. Our empirical analysis highlights the protocol’s enhanced resilience and efficiency under various conditions, while also addressing challenges related to scalability as the network size increases.
Quantum entanglement can be employed in some distributed communication tasks to reduce computation and communication overheads, yielding speedups over their classical counterparts. However, existing quantum Byzantine protocols often entail excessive communication and entanglement resource consumption. Conversely, classical schemes face insecurity with the impending reality of quantum computers. To address these challenges, we present a novel quantum Detectable Weak Byzantine Agreement (DWBA) protocol with high practicability, security and optimal fault-tolerance bound. For all n players, our protocol can complete the consensus of infinite classical information via fixed n + 1 -entangled qubits and a digest function, which requires infinite entanglement resources in previous schemes. Moreover, our protocol can tolerate arbitrary t ( t < n ) faulty players without necessitating any additional initial setup information (e.g., digital signature, private random coins). In terms of efficiency, our protocol only requires O (1) rounds and O ( ( n − t ) 2 ) communication complexity, constituting an order of magnitude improvement over previous protocols. In addition, the DWBA problem solved by our protocol is inherently stronger than the 3-player Detectable Byzantine Agreement (DBA) problem solved by previous protocols, and in a weaker but sufficiently practical model, our protocol can achieve Weak Byzantine Agreement (WBA).
In the burgeoning domain of distributed quantum computing, achieving consensus amidst adversarial settings remains a pivotal challenge. We introduce an enhancement to the Quantum Byzantine Agreement (QBA) protocol, uniquely incorporating advanced error mitigation techniques: Twirled Readout Error Extinction (T-REx) and dynamical decoupling (DD). Central to this refined approach is the utilization of a Noisy Intermediate Scale Quantum (NISQ) source device for heightened performance. Extensive tests on both simulated and real-world quantum devices, notably IBM's quantum computer, provide compelling evidence of the effectiveness of our T-REx and DD adaptations in mitigating prevalent quantum channel errors. Subsequent to the entanglement distribution, our protocol adopts a verification method reminiscent of Quantum Key Distribution (QKD) schemes. The Commander then issues orders encoded in specific quantum states, like Retreat or Attack. In situations where received orders diverge, lieutenants engage in structured games to reconcile discrepancies. Notably, the frequency of these games is contingent upon the Commander's strategies and the overall network size. Our empirical findings underscore the enhanced resilience and effectiveness of the protocol in diverse scenarios. Nonetheless, scalability emerges as a concern with the growth of the network size. To sum up, our research illuminates the considerable potential of fortified quantum consensus systems in the NISQ era, highlighting the imperative for sustained research in bolstering quantum ecosystems.
No system entity within a contemporary distributed cyber system can be entirely trusted. Hence, the classic centralized trust management method cannot be directly applied to it. Blockchain technology is essential to achieving decentralized trust management, its consensus mechanism is useful in addressing large-scale data sharing and data consensus challenges. Herein, an n-party quantum detectable Byzantine agreement (DBA) based on the GHZ state to realize the data consensus in a quantum blockchain is proposed, considering the threat posed by the growth of quantum information technology on the traditional blockchain. Relying on the nonlocality of the GHZ state, the proposed protocol detects the honesty of nodes by allocating the entanglement resources between different nodes. The GHZ state is notably simpler to prepare than other multi-particle entangled states, thus reducing preparation consumption and increasing practicality. When the number of network nodes increases, the proposed protocol provides better scalability and stronger practicability than the current quantum DBA. In addition, the proposed protocol has the optimal fault-tolerant found and does not rely on any other presumptions. A consensus can be reached even when there are n−2 traitors. The performance analysis confirms viability and effectiveness through exemplification. The security analysis also demonstrates that the quantum DBA protocol is unconditionally secure, effectively ensuring the security of data and realizing data consistency in the quantum blockchain.
Quantum networks comprised of entangled end nodes serve stronger than the classical correlation for unparalleled quantum internet applications. However, practical quantum networking is affected by noise, which at its worst, causes end nodes to be described by pre-existing classical data. In such untrusted networks, determining quantum network fidelity and genuine multi-node entanglement becomes crucial. Here, we show that determining quantum network fidelity and genuine N -node entanglement in an untrusted star network requires only N + 1 measurement settings. This method establishes a semi-trusted framework, allowing some nodes to relax their assumptions. Our network determination method is enabled by detecting genuine N -node Einstein-Podolsky-Rosen steerability. Experimentally, using spontaneous parametric down-conversion entanglement sources, we demonstrate the determinations of genuine 3-photon and 4-photon quantum networks and the false positives of the widely used entanglement witness, the fidelity criterion of 1/2. Our results provide a scalable method for the determination of multipartite entanglement in realistic quantum networks.