Superposition states two-atom systems

The eigenstates (35) are the collective states of two interacting atoms and are known in quantum optics as the Dicke states of the two-atom system [1]. We note here that the collective states s) and a) are an example of maximally entangled states of the two-atom system that the eigenstates of the system are linear superpositions which cannot be separated into product states of the individual atoms. 

---