Physical Review LettersPositivity Conditions for the Density Matrix of Spin-One ParticlesPierre MinnaertPublished Apr 11, 1966• 34 citationsPublisherAbstractReceived 17 February 1966DOI:https://doi.org/10.1103/PhysRevLett.16.672©1966 American Physical SocietyDOI10.1103/physrevlett.16.672