Atomic Wehrl entropy for the Jaynes–Cummings model: explicit form and Bloch sphere radius

For the interaction between a two-level atom and the radiation field in the dipole and the rotating wave approximations, namely, the Jaynes–Cummings model, we obtain a closed form for the atomic Wehrl entropy in terms of the Bloch sphere radius. This explains analytically why the atomic Wehrl entropy has an identical behavior to that of the von Neumann entropy.