  We study the Two Photon Quantum Rabi Model by way of its spectral functions
and survival probabilities. This approach allows numerical precision with large
truncation numbers, and thus exploration of the spectral collapse. We provide
independent checks and calibration of the numerical results by studying an
exactly solvable case and comparing the essential qualitative structure of the
spectral functions. We stress that the large time limit of the survival
probability provides us with an indicator of spectral collapse, and propose a
technique for the detection of this signal in the current and upcoming quantum
simulations of the model.
