Abstract
We extend the concept of classicality in quantum optics to spin states. We call a state “classical” if its density matrix can be decomposed as a weighted sum of angular momentum coherent states with positive weights. Classical spin states form a convex set , which we fully characterize for a spin and a spin 1. For arbitrary spin, we provide “nonclassicality witnesses.” For bipartite systems, forms a subset of all separable states. A state of two spins belongs to if and only if it is separable, whereas for a spin coupled to a spin 1, there are separable states which do not belong to . We show that in general the question whether a state is in can be answered by a linear programming algorithm.
- Received 16 May 2008
DOI:https://doi.org/10.1103/PhysRevA.78.042112
©2008 American Physical Society