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Multiple fidelities and joint numerical range

arXiv Quantum Physics
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⚡ Quantum Brief
Researchers Pei Li and Bang-Hai Wang introduced a geometric framework using joint separable numerical ranges to improve entanglement detection via multiple fidelities, published May 2026. They established a necessary and sufficient criterion for detection when reference states are product states: either a pair must have nontrivial local inner product moduli or the reference states’ orthogonal complement must be fully entangled. The study reveals sets of product states where no subset detects entanglement, but the full set does—exemplified by unextendible product bases, a first in entanglement witness design. For bipartite systems, they fully characterized joint numerical ranges for two reference product states, proving the separable range depends only on local fidelities, demonstrated via a two-qubit case. This work provides a systematic method to construct entanglement witnesses and extends foundational tools for higher-dimensional and multipartite quantum systems.
Multiple fidelities and joint numerical range

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Quantum Physics arXiv:2605.24360 (quant-ph) [Submitted on 23 May 2026] Title:Multiple fidelities and joint numerical range Authors:Pei Li, Bang-Hai Wang View a PDF of the paper titled Multiple fidelities and joint numerical range, by Pei Li and Bang-Hai Wang View PDF HTML (experimental) Abstract:We investigate the effectiveness of entanglement detection based on multiple fidelities via the geometry of the joint separable numerical range. When all reference states are product states, we derive a necessary and sufficient criterion for such detection: either some pair of reference states has nontrivial moduli of the local inner products on both subsystems, or the orthogonal complement of the span of the reference states is completely entangled. We further show that there exist sets of reference product states for which no proper subset is effective for entanglement detection, whereas the full set is. A typical example of this phenomenon is provided by unextendible product bases. Moreover, for a pair of reference product states on a bipartite system with arbitrary local dimensions, we characterize both the joint numerical range and the joint separable numerical range, showing that the joint separable numerical range is determined solely by their local fidelities, as illustrated by a representative two-qubit example. Our results offer a systematic approach to designing effective entanglement witnesses and lay the groundwork for extensions to higher-dimensional and multipartite scenarios. Comments: Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2605.24360 [quant-ph] (or arXiv:2605.24360v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2605.24360 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Bang-Hai Wang [view email] [v1] Sat, 23 May 2026 02:52:12 UTC (108 KB) Full-text links: Access Paper: View a PDF of the paper titled Multiple fidelities and joint numerical range, by Pei Li and Bang-Hai WangView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-05 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?) 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