Evaluating the Impact of Gate Errors on a Quantum-Aided Byzantine Agreement Protocol

Abstract

The Byzantine agreement problem in computer science focuses on honest parties trying to achieve consensus in a network with malicious actors. The performance of a quantum-aided Byzantine agreement protocol was evaluated under more realistic noise conditions, with a particular focus on gate-level errors. Since quantum systems are affected by various forms of noise, understanding the impact of quantum noise is crucial for assessing the practical viability and robustness of such protocols. Our results indicate a gate error probability threshold of 0.001%, below which the protocol maintains a failure probability of less than 5%. However, only a single source of noise was considered, with the depolarizing probabilities for single- and two-qubit gates assumed to be equal. This noise level closely matches the currently achievable error rate for single-qubit gates, but is over an order of magnitude lower than that for two-qubit gates on quantum network hardware. Consequently, our findings suggest that the protocol, in its current form, requires further research before it can be deployed on existing quantum devices. Moreover, the results strongly indicate that two-qubit gate errors are the primary bottleneck. These results highlight the significant impact of quantum noise on distributed quantum protocols and underscore the need for either improved quantum hardware or enhanced fault-tolerant protocol designs.