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Hardy nonlocality for entangled pairs in a four-particle system

arXiv Quantum Physics
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⚡ Quantum Brief
Researchers Duc Manh Doan and Hung Q. Nguyen demonstrated Hardy nonlocality in a novel four-particle cyclic entanglement structure, where each particle entangles only with its two neighbors, unlike prior fully entangled systems. Their study reveals this configuration yields more contradictions with local hidden variable (LHV) models due to multiple excluded states, enhancing nonlocality detection without relying on Bell inequalities. The team designed quantum circuits matching the cyclic structure, simulating correlation patterns to identify key states, offering a theoretical framework for experimental validation. When tested on IBM Brisbane’s quantum hardware, results deviated significantly from simulations, highlighting current limitations in practical implementations of complex entanglement structures. This work expands Hardy’s paradox beyond fully entangled systems, suggesting cyclic configurations could strengthen nonlocality tests in quantum information protocols.
Hardy nonlocality for entangled pairs in a four-particle system

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Quantum Physics arXiv:2601.04636 (quant-ph) [Submitted on 8 Jan 2026] Title:Hardy nonlocality for entangled pairs in a four-particle system Authors:Duc Manh Doan, Hung Q. Nguyen View a PDF of the paper titled Hardy nonlocality for entangled pairs in a four-particle system, by Duc Manh Doan and 1 other authors View PDF HTML (experimental) Abstract:Nonlocality can be studied through different approaches, such as Bell's inequalities, and it can be found in numerous quantum states, including GHZ states or graph states. Hardy's paradox, or Hardy-type nonlocality, provides a way to investigate nonlocality for entangled states of particles without using inequalities. Previous studies of Hardy's nonlocality have mostly focused on the fully entangled systems, while other entanglement configurations remain less explored. In this work, the system under investigation consists of four particles arranged in a cyclic entanglement configuration, where each particle forms entangled pairs with two neighbors, while non-neighboring particles remain unentangled. We found that this entanglement structure offers a larger set of conditions that lead to the contradiction with the LHV model, compared to the fully entangled systems. This enhancement can be attributed to the presence of multiple excluded states and correlations, in which the measurement result of a particle only influences the result of its paired partners. We implement quantum circuits compatible with the cyclic entanglement structure, and through simulation, the correlation patterns and the states of interest are identified. We further execute the proposed circuits on IBM Brisbane, a practical backend; however, the results show considerable deviations from the simulation counterparts. Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2601.04636 [quant-ph] (or arXiv:2601.04636v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2601.04636 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Hung Nguyen [view email] [v1] Thu, 8 Jan 2026 06:14:12 UTC (2,875 KB) Full-text links: Access Paper: View a PDF of the paper titled Hardy nonlocality for entangled pairs in a four-particle system, by Duc Manh Doan and 1 other authorsView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-01 References & Citations INSPIRE HEP NASA ADSGoogle Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... Data provided by: Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv (What is alphaXiv?) Links to Code Toggle CatalyzeX Code Finder for Papers (What is CatalyzeX?) DagsHub Toggle DagsHub (What is DagsHub?) GotitPub Toggle Gotit.pub (What is GotitPub?) Huggingface Toggle Hugging Face (What is Huggingface?) Links to Code Toggle Papers with Code (What is Papers with Code?) ScienceCast Toggle ScienceCast (What is ScienceCast?) Demos Demos Replicate Toggle Replicate (What is Replicate?) Spaces Toggle Hugging Face Spaces (What is Spaces?) Spaces Toggle TXYZ.AI (What is TXYZ.AI?) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower (What are Influence Flowers?) Core recommender toggle CORE Recommender (What is CORE?) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them. Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs. Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)

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Source: arXiv Quantum Physics