Solution of the two-mode quantum Rabi model using extended squeezed states
Liwei Duan, Shu He, Daniel Braak, Qing‐Hu Chen · Europhysics Letters (EPL) · 2015
The two-mode quantum Rabi model with bilinear coupling is studied using extended squeezed states. We derive G -functions for each Bargmann index q . They share a common structure with the G -function of the one-photon and two-photon quantum Rabi models. The regular spectrum is given by zeros of the G -function while the conditions for the presence of doubly degenerate (exceptional) eigenvalues are obtained in closed form through the lifting property. The simple singularity structure of the G -function allows to draw conclusions about the distribution of eigenvalues along the real axis and to understand the spectral collapse phenomenon when the coupling reaches a critical value.