Polytopes of Absolutely Wigner Bounded Spin States

We study the properties of unitary orbits of mixed spin states that are characterized by Wigner functions lower bounded by a specified value. To this end, we extend a characterization of the set of absolutely Wigner positive states as a set of linear eigenvalue constraints, which together define a polytope in the simplex of spin-j mixed states centred on the maximally mixed state. The lower bound determines the relative size of such absolutely Wigner bounded (AWB) polytopes and we study their geometric properties. In particular, in each dimension a Hilbert-Schmidt ball representing a tight AWB sufficiency criterion based on the purity is exactly determined. Special attention is given to the case where the polytope separates orbits containing only positive Wigner functions from other orbits because of the use of Wigner negativity as a witness of non-classicality of spin states. Comparisons are made to absolute symmetric state separability and spherical Glauber-Sudarshan positivity, with additional details given for low spin quantum numbers.

[1] J. Denis, J. Davis, R. B. Mann, and J. Martin, arXiv:2304.09006.