Forbidden Subspaces in Quantum State Smoothing

Abstract:A system between a preparation and a post-selection has had no agreed state since 1964. With positivity as the criterion, a post-selection admits an interval of orderings around the symmetric one exactly when the subspace it forbids is spanned by eigenvectors of a full-rank filtered state. Otherwise it certifies contextuality, testable on a qubit. The averaged filtered state carries the entanglement spectrum of the record, so the smallest forbidden subspaces a symmetry allows are even-dimensional in the Haldane class and odd in the trivial one. That parity is the record's topological class.

9 pages, 2 figures, REVTeX 4.2

arXiv:2609.17307 [quant-ph]

(or arXiv:2609.17307v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2609.17307 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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