“…In fact, the Dicke model with j ≥ 1 for nonzero energy splitting between the two levels of the single atom is formally not integrable when λ/ω 0 → ∞, though the model is exactly solvable and integrable when j = 1/2, as recently pointed out by Braak [16,20]. Braak's exact solution to the Dicke model with j = 1/2 was also recovered [50,51] by using the Bogoliubov operators and the method proposed in [22], respectively, while the finite size Dicke model was also studied within the shifted boson basis in [52], which confirms Braak's observations on the exact solvability of the Dicke model, though the model is not integrable in general. However, the Poissonian limit is reached as λ/ω 0 → ∞ at the resonance point, which is also demonstrated in [10].…”