  We investigate analytically and numerically the nonstationary circuit QED
setup in which $N$ independent qubits interact with a single mode of the
Electromagnetic field confined in a resonator. We consider the harmonic time
modulation of some parameter (atomic transition frequency or the atom-field
coupling strength) and derive the unitary dynamics up to the second order in
the modulation depth for $N=1$ and $N\gg 1$. It is shown that all the resonant
phenomena that occur for modulation frequencies $\sim 2\omega _{0}$ (where
$\omega _{0}$ is the cavity frequency) also occur for the halved frequencies.
However, in the latter case the associated transition rates are significantly
smaller and the modulation of the coupling strength is less effective. The
transition rates are evaluated explicitly and the prospects of employing the
second-order resonances in the phenomena related to the dynamical Casimir
effect are examined.
