The Landau-Feynman Transiently Open Quantum System: Entanglement and Density Operators

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...

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Bibliographic Details
Published inInformation (Basel) Vol. 16; no. 7; p. 558
Main Authors Deville, Alain, Deville, Yannick
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.07.2025
Subjects
bipartite system
Density
density operator
entanglement
improper mixture
Quantum entanglement
Quantum mechanics
Quantum physics
quantum state tomography
Quantum theory
Tomography
transient coupling
United Kingdom
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Summary: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.
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ISSN:2078-2489
2078-2489
DOI:10.3390/info16070558