Figure 3
From: Analytical Solution for the Anisotropic Rabi Model: Effects of Counter-Rotating Terms

The absolute value of the Bloch-Siegert shift with the transition E1− → EG as a function of g and g′ for ω = 1, Ω = 0.3.
The part (a) represents the analytical results, while the part (b) corresponds to the numerical results.