CPDNN quantum channels with qubit output are CPCP
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Quantum Physics arXiv:2603.16962 (quant-ph) [Submitted on 17 Mar 2026] Title:CPDNN quantum channels with qubit output are CPCP Authors:Hyunho Cha View a PDF of the paper titled CPDNN quantum channels with qubit output are CPCP, by Hyunho Cha View PDF HTML (experimental) Abstract:The resource theory for nonnegativity of quantum amplitudes distinguishes completely positive completely positive (CPCP) quantum channels from the larger and more tractable class of completely positive doubly nonnegative (CPDNN) quantum channels. It was left open whether there exists a qutrit-to-qubit quantum channel \(\Phi:M_3\to M_2\) that is CPDNN but not CPCP. We answer this question in the negative and prove the stronger statement that every CPDNN quantum channel \(\Phi:M_n\to M_2\) is CPCP for every \(n\in\mathbb N\). Equivalently, for qubit-output quantum channels the doubly nonnegative relaxation is exact. Comments: Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2603.16962 [quant-ph] (or arXiv:2603.16962v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2603.16962 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Hyunho Cha [view email] [v1] Tue, 17 Mar 2026 06:22:31 UTC (5 KB) Full-text links: Access Paper: View a PDF of the paper titled CPDNN quantum channels with qubit output are CPCP, by Hyunho ChaView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-03 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?)