Unified approach to various quantum Rabi models with arbitrary parameters
Dong Xiao-Fei1, Xie You-Fei1, Chen Qing-Hu1, 2, †
       

A few low levels for Δ = 0.5, U = 0.5, r = 0.1 by both the closed form (filled circles) and the exact solutions by zeros of Eq. (7) (solid lines). Level crossing appears for both cases.