  Computing the entanglement of formation of a bipartite state is generally
difficult, but special symmetries of a state can simplify the problem. For
instance, this allows one to determine the entanglement of formation of Werner
states and isotropic states. We consider a slightly more general class of
states, rotationally symmetric states, also known as SU(2)-invariant states.
These states are invariant under global rotations of both subsystems, and one
can examine entanglement in cases where the subsystems have different
dimensions. We derive an analytic expression for the entanglement of formation
of rotationally symmetric states of a spin-$j$ particle and a spin-${1\over2}$
particle. We also give expressions for the I-concurrence, I-tangle, and
convex-roof-extended negativity.
