Absolutely classical spin states
Fabian Bohnet-Waldraff, Olivier Giraud, Daniel Braun · Physical Review A · 2017
We introduce the concept of ``absolutely classical'' spin states, in analogy to absolutely separable states of bipartite quantum systems. Absolutely classical states are states that remain classical (i.e., a convex sum of projectors on coherent states of a spin $j$) under any unitary transformation applied to them. We investigate the maximal size of the ball of absolutely classical states centered on the maximally mixed state and derive a lower bound for its radius as a function of the total spin quantum number. We also obtain a numerical estimate of this maximal radius and compare it to the case of absolutely separable states.