  Artificial atoms (AA) offer the possibility to design physical systems
implementing new regimes of ultrastrong coupling (USC) between radiation and
matter, where previously unexplored non-perturbative physics emerges. While
experiments so far provided only spectroscopic evidence of USC, we propose the
dynamical detection of virtual photon pairs in the dressed eigenstates, which
is a "smoking gun" of the very existence of USC in nature. We show how to
coherently amplify this channel to reach 100% efficiency by operating advanced
control similar to stimulated Raman adiabatic passage (STIRAP).
