Generation of photons from vacuum in cavity via time-modulation of a qubit invisible to the field

We propose a scheme for generation of photons from vacuum due to time-modulation of a quantum system coupled indirectly to the cavity field through some ancilla quantum subsystem. We consider the simplest case when the modulation is applied to an artificial 2-level atom (we call t-qubit), while the ancilla is a stationary qubit coupled via the dipole interaction both to the cavity and t-qubit. We find that tripartite entangled states with a small number of photons can be generated from the system ground state under resonant modulations, even when the t-qubit is far detuned from both the ancilla and the cavity, provided its bare and modulation frequencies are properly adjusted as function of other system parameters. We attest our approximate analytic results by numeric simulations and show that photon generation from vacuum persists in the presence of common dissipation mechanisms.