  The ground state of a pair of ultrastrongly coupled bosonic modes is
predicted to be a two-mode squeezed vacuum. However, the corresponding quantum
correlations are currently unobservable in condensed matter where such a
coupling can be reached, since it cannot be extracted from these systems. Here,
we show that superconducting circuits can be used to perform an analog
simulation of a system of two bosonic modes in regimes ranging from strong to
ultrastrong coupling. More importantly, our quantum simulation setup enables us
to detect output excitations that are related to the ground-state properties of
the bosonic modes. We compute the emission spectra of this physical system and
show that the produced state presents single- and two-mode squeezing
simultaneously.
