  We consider the generalized quantum Rabi model with the so-called
$A^{2}$-term in the light of the Hepp-Lieb-Preparata quantum phase transition.
We investigate the dressed photon in its ground state when the atom-light
coupling strength is in the deep-strong coupling regime. We show how the
dressed photon appears in the ground state. We dedicate this paper to Pavel
Exner and Herbert Spohn on the occasion of their 70th birthdays, and Klaus Hepp
on the occasion of his 80th birthday.
