In distributed computing, a Byzantine fault is a condition where a component behaves inconsistently, showing different symptoms to different components of the system. Consensus among the correct components can be reached by appropriately crafted communication protocols even in the presence of byzantine faults. Quantum-aided protocols built upon distributed entangled quantum states are worth considering, as they are more resilient than traditional ones. Based on earlier ideas, here we establish a parameter-dependent family of quantum-aided weak broadcast protocols. We compute upper bounds on the failure probability of the protocol, and define and illustrate a procedure that minimizes the quantum resource requirements. Following earlier work demonstrating the suitability of noisy intermediate scale quantum (NISQ) devices for the study of quantum networks, we experimentally create our resource quantum state on publicly available quantum computers. Our work highlights important engineering aspects of the future deployment of quantum communication protocols with multi-qubit entangled states.
In distributed computing, a Byzantine fault is a condition where a component behaves inconsistently, showing different symptoms to different components of the system. Consensus among the correct components can be reached by appropriately crafted communication protocols even in the presence of byzantine faults. Quantum-aided protocols built upon distributed entangled quantum states are worth considering, as they are more resilient than traditional ones. Based on earlier ideas, here we establish a parameter-dependent family of quantum-aided weak broadcast protocols. We compute upper bounds on the failure probability of the protocol, and define and illustrate a procedure that minimizes the quantum resource requirements. Following earlier work demonstrating the suitability of noisy intermediate scale quantum (NISQ) devices for the study of quantum networks, we experimentally create our resource quantum state on publicly available quantum computers. Our work highlights important engineering aspects of the future deployment of quantum communication protocols with multi-qubit entangled states.
This paper proposes a novel distributed consensus algorithm utilizing quantum entanglement to achieve Byzantine fault tolerance. Traditional consensus algorithms struggle to guarantee correctness in the face of malicious actors (Byzantine faults) where nodes can arbitrarily deviate from the honest majority. This work introduces a protocol that leverages the unique properties of quantum entanglement to establish correlated states between nodes, enabling the detection and mitigation of these malicious behaviors without relying on trusted third parties or computationally intensive verification processes. The core claim is that quantum entanglement provides a provably secure and efficient mechanism for distributed consensus, offering superior resilience compared to classical approaches. The algorithm is formally described, and key mathematical components, including state transformations and probability calculations, are presented. The theoretical analysis demonstrates the algorithm's ability to converge to a correct consensus state even when a significant fraction of nodes are faulty. The use of entanglement fundamentally alters the Byzantine fault tolerance landscape, offering a pathway towards more robust and secure distributed systems.
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).
We design and experimentally validate quantum circuits that prepare a quantum resource state which, when combined with authenticated classical communication, enables a protocol for detectable Byzantine broadcast and detectable Byzantine consensus. For the broadcast version of the problem, we propose an efficient leader-follower quantum circuit that prepares this resource state with depth O(logn), using O(n) two-qubit gates and O(n) ancillary qubits. We also develop a majority-based leader-selection scheme, for the consensus version of the problem; the scheme is based on the same leaderfollower quantum circuit and on coherent Hamming-weight computation, which prepares a fictitious leader qubit directly from any initial network state specified by the participant parties. The resulting fictitious leader state is then used as input to the leader-follower circuit to prepare a resource state consistent with majority voting on a common basis, thereby enabling detectable Byzantine consensus. In particular, we prove that, when supplemented with authenticated classical channels for the communication of quantum measurement outputs, the resulting protocols achieve detectable Byzantine broadcast and detectable Byzantine consensus, respectively. Under correct operation, all correct parties output the same value, namely the leader's value or the majority value. In the presence of Byzantine parties or quantum circuit deviations, all correct parties detect the inconsistency and abort. Furthermore, we demonstrate the feasibility of the approach through a proofof-principle implementation on an IBM quantum processor.
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.
This paper presents a novel approach to distributed consensus protocols leveraging quantum entanglement and Byzantine fault tolerance. The core claim is that quantum entanglement can provide secure and efficient agreement among nodes even in the presence of malicious actors. We propose a mechanism that utilizes quantum key distribution (QKD) to establish shared entanglement between participating nodes. Subsequent quantum measurements identify faulty nodes, informing a robust consensus algorithm built upon majority voting and entanglement-based error correction. The potential advantages of this combined approach – enhanced security and efficiency compared to traditional classical methods – are explored. The research addresses the critical challenge of achieving reliable consensus in distributed systems susceptible to Byzantine attacks. This work introduces a new paradigm for consensus, potentially leading to more resilient and secure distributed applications.
Byzantine agreement, the underlying core of blockchain, aims to make every node in a decentralized network reach consensus. Classical Byzantine agreements unavoidably face two major problems. One is 1/3 fault-tolerance bound, which means that the system to tolerate f malicious players requires at least 3 f + 1 players. The other is the security loopholes from its classical cryptography methods. Here, we propose a Byzantine agreement framework with unconditional security to break this bound with nearly 1/2 fault tolerance due to multiparty correlation provided by quantum digital signatures. It is intriguing that quantum entanglement is not necessary to break the 1/3 fault-tolerance bound, and we show that weaker correlation, such as asymmetric relationship of quantum digital signature, can also work. Our work strictly obeys two Byzantine conditions and can be extended to any number of players without requirements for multiparticle entanglement. We experimentally demonstrate three-party and five-party consensus for a digital ledger. Our work indicates the quantum advantage in terms of consensus problems and suggests an important avenue for quantum blockchain and quantum consensus networks.