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

Multipartite Quantum Cryptography

Nicolas Laurent-Puig, Laura dos Santos Martins, Matilde Baroni, Santiago Schneider, Luís Bugalho, Majid Hassani, Sean William Moore, Damian Markham, Eleni Diamanti

Published Apr 6, 2026• 0 citations
Publisher

Abstract

Quantum networks provide a powerful platform for implementing protocols that outperform their classical counterparts in both functionality and security. To realize their full potential, however, it is essential to ensure they are secure, efficient, and experimentally viable. Using high-fidelity polarization-encoded 4-qubit GHZ states generated in a compact double-layer Sagnac interferometer, we experimentally implement a privacy-preserving distributed phase estimation protocol, enabling the reconstruction of a global function without revealing the local information of individual network users. Furthermore, we also implement an information-theoretically secure voting protocol that requires no election authorities and extend its functionality to combine privacy and support for multiple candidates and voter pools. Our results showcase versatile quantum protocols that can address key challenges in secure computation, quantum voting, and quantum networks, all within a practical experimental framework.

DOI
10.1109/qcnc69040.2026.00089

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Quantum networks provide a powerful platform for implementing protocols that outperform their classical counterparts in both functionality and security. To realize their full potential, however, it is essential to ensure they are secure, efficient, and experimentally viable. Using high-fidelity polarization-encoded 4-qubit GHZ states generated in a compact double-layer Sagnac interferometer, we experimentally implement a privacy-preserving distributed phase estimation protocol, enabling the reconstruction of a global function without revealing the local information of individual network users. Furthermore, we also implement an information-theoretically secure voting protocol that requires no election authorities and extend its functionality to combine privacy and support for multiple candidates and voter pools. Our results showcase versatile quantum protocols that can address key challenges in secure computation, quantum voting, and quantum networks, all within a practical experimental framework.
Quantum information protocols offer significant advantages in properties such as security, anonymity, and privacy for communication and computing tasks. An application where guaranteeing the highest possible security and privacy is critical for democratic societies is electronic voting. As computational power continues to evolve, classical voting schemes may become increasingly vulnerable to information leakage. In this work, we present the experimental demonstration of an information-theoretically secure and efficient electronic voting protocol that, crucially, does not rely on election authorities, leveraging the unique properties of quantum states. Our experiment is based on a high-performance source of Greenberger-Horne-Zeilinger (GHZ) states and realizes a proof-of-principle implementation of the protocol in two scenarios: a configuration with four voters and two candidates employing privacy enhancement techniques and an election scenario supporting up to eight voters and sixteen candidates. The latter is particularly well-suited for secure board-level elections within organizations or small-scale governmental contexts.
Quantum communication protocols seek to leverage the unique properties of quantum systems for coordination or communication tasks, usually with guarantees of security or anonymity that exceed what is possible classically. One promising domain of application is elections, where strong such guarantees are essential to ensure legitimacy. We experimentally implement a recently proposed election protocol from Centrone et al. such that no one, including a potential central authority, can know the preferred candidate of any voter other than themself. We conduct a four-party election, generating and distributing four-partite GHZ states with ≈89%\approx 89\%≈89% fidelity and successfully recording voters' intentions ≈87%\approx 87\%≈87% of the time.
Electronic voting is a very useful but challenging internet-based protocol that despite many theoretical approaches and various implementations with different degrees of success, remains a contentious topic due to issues in reliability and security. Here we present a quantum protocol that exploits an untrusted source of multipartite entanglement to carry out an election without relying on election authorities, simultaneous broadcasting or computational assumptions, and whose result is publicly verifiable. The level of security depends directly on the fidelity of the shared multipartite entangled quantum state, and the protocol can be readily implemented for a few voters with state-of-the-art photonic technology.
Quantum communication protocols seek to leverage the unique properties of quantum systems for coordination or communication tasks, usually with guarantees of security or anonymity that exceed what is possible classically. One promising domain of application is elections, where strong such guarantees are essential to ensure legitimacy. We experimentally implement a recently proposed election protocol from Centrone et al. [Quantum protocol for electronic voting without election authorities, Phys. Rev. Appl. 18, 014005 (2022)PRAHB22331-701910.1103/PhysRevApplied.18.014005] designed such that no one, including a potential central authority, can know the preferred candidate of any voter other than themself. We conduct a four-party election, generating and distributing four-partite GHZ states with ≈89% fidelity and successfully recording voters' intentions ≈87% of the time.
Entangling distant quantum sensors is a key application of future quantum networks, allowing for the estimation of global functions of local parameters, with precision that is not possible with stand-alone, individual, quantum sensors. However, with this advantage comes the risk of information leakage over the network via possible malicious parties. It is often particularly important that local parameters remain unknown and that only the global function is shared across the network. Recently, the notion of privacy has been introduced in this context, which ensures that only the agreed function of parameters is shared over the network, even when malicious parties control the network itself, whilst maintaining the estimation advantage. In this work, we introduce a noise-robust protocol for private quantum networked sensing, which we realise using a high-fidelity Greenberger-Horne-Zeilinger (GHZ) state source. We further run a comparative analysis and simulate attacks using three different quantum states, a four-qubit GHZ state, two Bell pairs, and a fully separable state. Our results highlight the clear advantage of GHZ states in maintaining high precision, accuracy, and privacy for the distributed estimation task.
Electronic voting is a very useful but challenging internet-based protocol that despite many theoretical approaches and various implementations with different degrees of success, remains a contentious topic due to issues in reliability and security. Here we present a quantum protocol that exploits an untrusted source of multipartite entanglement to carry out an election without relying on election authorities, simultaneous broadcasting, or computational assumptions, and whose result is publicly verifiable. The level of security depends directly on the fidelity of the shared multipartite entangled quantum state, and the protocol can be readily implemented for a few voters with state-of-the-art photonic technology.