Disproving hidden variable models with spin magnitude conservation

Paweł Kurzyński, Wiesław Laskowski, Adrian Kołodziejski, Károly F. Pál, Junghee Ryu, Tamás Vértesi

Research output: Contribution to journalArticle


The squares of the three components of the spin-s operators sum up to s(s + 1). However, a similar relation is rarely satisfied by the set of possible spin projections onto mutually orthogonal directions. This has fundamental consequences if one tries to construct a hidden variable (HV) theory describing measurements of spin projections. We propose a test of local HV models in which spin magnitudes are conserved. These additional constraints imply that the corresponding inequalities are violated within quantum theory by larger classes of correlations than in the case of standard Bell inequalities. We conclude that in any HV theory pertaining to measurements on a spin one can find situations in which either HV assignments do not represent a physical reality of a spin vector, but rather provide a deterministic algorithm for prediction of the measurement outcomes, or HV assignments represent a physical reality, but the spin cannot be considered as a vector of fixed length.

Original languageEnglish
Article number15
JournalCommunications Physics
Issue number1
Publication statusPublished - Dec 1 2019


ASJC Scopus subject areas

  • Physics and Astronomy(all)

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