Classicality of spin-coherent states via entanglement and distinguishability

Abstract

We investigate the classical nature of the spin coherent states. In addition to being minimum uncertainty states, as the size of the spin, S, increases, the classical nature is seen to increase in two respects: in their resistance to entanglement generation (when passed through a beam splitter) and in the distinguishability of the states. In the infinite S limit the spin coherent state is a subclass of the optical coherent states (namely the subclass of orthogonal optical coherent states). These states generate no entanglement and are obviously completely distinguishable. The decline of the generated entanglement, and in this sense increase in classicality with S, is very slow and dependent on the amplitude z of the state. Surprisingly we find that for |z| > 1 there is an initial increase in entanglement followed by an extremely gradual decline to zero. The distinguishability, on the other hand, quickly becomes classical for all z. We illustrate the distinguishability of spin coherent states in a novel manner using the representation of Majorana.