The dynamical Casimir effect which predicts photon production from vacuum is a noteworthy example of the nonadiabatic effect in quantum field theory. Unfortunately, this effect has not yet been confirmed experimentally since 1970.
Here we propose a novel scheme for confirming the dyanamical Casimir effect using a Josephson artificial atom with high external-field response and its strong coupling to photon fields. In addition, we found both analytically and numerically that generated quantum states due to nonadiabatic effect are squeezed vacuum states with peculiar probability distribution. This provides a strong evidence instead of conventional photon-detection scheme.