{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T01:28:04Z","timestamp":1760059684623,"version":"build-2065373602"},"reference-count":20,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,6,30]],"date-time":"2025-06-30T00:00:00Z","timestamp":1751241600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Information"],"abstract":"<jats:p>Users of quantum mechanics are familiar with the concept of a statistical mixture as introduced by von Neumann, and with the use of a density operator in that context. A density operator may also be used in another situation, introduced by Landau, with a transient coupling between the two parts of a quantum bipartite system. But more than fifty years after a clarifying work by Feynman on the subject, a confusion still persists about what we call the Landau-Feynman situation. In this paper we establish that, when facing that situation, the right concept to be used is not the one of a mixed state - be it qualified as proper or improper -, but the one of entanglement.<\/jats:p>","DOI":"10.3390\/info16070558","type":"journal-article","created":{"date-parts":[[2025,6,30]],"date-time":"2025-06-30T13:06:17Z","timestamp":1751288777000},"page":"558","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The Landau-Feynman Transiently Open Quantum System: Entanglement and Density Operators"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5246-8391","authenticated-orcid":false,"given":"Alain","family":"Deville","sequence":"first","affiliation":[{"name":"Aix-Marseille Universit\u00e9, CNRS, IM2NP UMR 7334, F-13397 Marseille, France"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8769-2446","authenticated-orcid":false,"given":"Yannick","family":"Deville","sequence":"additional","affiliation":[{"name":"IRAP (Institut de Recherche en Astrophysique et Plan\u00e9tologie), Universit\u00e9 de Toulouse, CNRS, CNES, OMP, F-31400 Toulouse, France"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Deville, A., and Deville, Y. 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Physique Quantique, EDP Sciences, Les Ulis\/CNRS Editions. [2nd ed.]. English version: Quantum Physics; Cambridge University Press: Cambridge, UK, 2006."},{"key":"ref_18","unstructured":"Kirkpatrick, K.A. (2004). Error in an argument regarding \u201cimproper\u201d mixtures. arXiv."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Breuer, H.P., and Petruccione, F. (2002). The Theory of Open Quantum Systems, Oxford University Press.","DOI":"10.1007\/3-540-44874-8_4"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1311","DOI":"10.1007\/s11128-011-0273-7","article-title":"Classical-processing and quantum-processing signal separation methods for qubit uncoupling","volume":"11","author":"Deville","year":"2012","journal-title":"Quantum Inf. Process."}],"container-title":["Information"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2078-2489\/16\/7\/558\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T18:01:50Z","timestamp":1760032910000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2078-2489\/16\/7\/558"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,6,30]]},"references-count":20,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2025,7]]}},"alternative-id":["info16070558"],"URL":"https:\/\/doi.org\/10.3390\/info16070558","relation":{},"ISSN":["2078-2489"],"issn-type":[{"type":"electronic","value":"2078-2489"}],"subject":[],"published":{"date-parts":[[2025,6,30]]}}}