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International Conference on Quantum Communications, Networking, and Computing (QCNC)

W-State Leader Election for PBFT Based Quantum Leader Election

Juan Pablo Robledo Meza, Jelena Mišić, Vojislav B. Mišić

Published Apr 6, 2026• 1 citation
Publisher

Abstract

We propose a quantum leader election protocol for high-traffic permissioned blockchains, leveraging multipartite$W$-states combined with a CSMA/CA-style INTENT/ACK handshake. Our design distributes a full W-state locally to each validator, enabling collision detection through single-qubit measurement and ensuring fairness without requiring global entanglement distribution. We formalize three approaches to improve performance, Exponential Backoff, Fixed$W$-state, and Closing Window, respectively, and analyze their expected termination times, showing that the Closing Window variant provides the best convergence behavior. Using Qiskit simulations, we evaluate correctness and demonstrate that$W$-state-based election integrates naturally with PBFT-style consensus layers.

DOI
10.1109/qcnc69040.2026.00182

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We propose a quantum leader election protocol for high-traffic permissioned blockchains, leveraging multipartiteWWW-states combined with a CSMA/CA-style INTENT/ACK handshake. Our design distributes a full W-state locally to each validator, enabling collision detection through single-qubit measurement and ensuring fairness without requiring global entanglement distribution. We formalize three approaches to improve performance, Exponential Backoff, FixedWWW-state, and Closing Window, respectively, and analyze their expected termination times, showing that the Closing Window variant provides the best convergence behavior. Using Qiskit simulations, we evaluate correctness and demonstrate thatWWW-state-based election integrates naturally with PBFT-style consensus layers.
We propose a scalable quantum architectures which can improve operation of Blockchain systems. We focus on permissioned blockchains with consensus derived from Practical Byzantine Fault Tolerance (PBFT). We propose multipartite entanglement quantum architectures that can perform PBFT. Further we develop quantum systems and algorithms that can support Proof of Stake (PoS) voting as well as voter election and voting in delegated Proof of Stake systems. Validating nodes within a cluster hold qubits entangled in multipartite structure. Due to maximally connected entanglement they jointly perform voting and calculate voting results. We propose algorithms that can track voter's behavior and detect collusion and voting centralization problem.
In developing quantum-classical network infrastructures, where coordination, entanglement distribution, and time-sensitive control rely on a stable and reliable coordinator, reliable leader election is crucial. In this work, we present VIKOR-BFT, a leader election scheme that integrates a lightweight data-sanitization stage with the VIKOR multi-criteria ranking mechanism to improve resilience against Byzantine behaviour. To understand its practical behaviour, we developed a Python-based prototype and evaluated the protocol under a range of adversarial and high-load scenarios. The study indicates that VIKOR-BFT keeps latency growth moderate even as the network scales and sustains throughput values above 100 tx/s in networks of roughly 500 nodes. In comparison with PBFT and an optimized PBFT variant, the proposed method reduces message complexity by almost two orders of magnitude without compromising the correctness of leader selection. Under 15% and 25% Byzantine participation, the protocol continues to select an honest leader in more than 90% and 75% of the trials, respectively. Overall, the findings suggest that VIKOR-BFT provides a scalable and practically viable option for secure leader election in hybrid quantum-classical communication environments.
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I show that WWW-like entangled quantum states are not a necessary quantum resource for totally correct anonymous leader election protocols. This is proven by defining a symmetric quantum state that is nnn-partite SLOCC inequivalent to the WWW state, and then constructing a totally correct anonymous leader election protocol using this state. This result, which contradicts the previous necessity result of D'Hondt and Panangaden, furthers our understanding of how non-local quantum states can be used as a resource for distributed computation.
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In this paper we show that sufficient multi-partite quantum entanglement helps in fair and unbiased election of a leader in a distributed network of processors with only linear classical communication complexity. We show that a total of O(log⁡n)O(\log n)O(logn) distinct multi-partite maximally entanglement sets (ebits) are capable of supporting such a protocol in the presence of nodes that may lie and thus be biased. Here, nnn is the number of nodes in the network. We also demonstrate the difficulty of performing unbiased and fair election of a leader with linear classical communication complexity in the absence of quantum entanglement even if all nodes have perfect random bit generators. We show that the presence of a sufficient number O(n/log⁡n)O(n/\log n)O(n/logn) of biased agents leads to a non-zero limiting probability of biased election of the leader, whereas, the presence of a smaller number O(log⁡n)O(\log n)O(logn) of biased agents matters little. We define two new related complexity classes motivated by the our leader election problem and discuss a few open questions.