Abstract
We map the quantum problem of a free bosonic field in a space-time dependent background into a classical problem. N degrees of freedom of a real field in the quantum theory are mapped into 2N² classical simple harmonic oscillators with specific initial conditions. We discuss how this classical-quantum correspondence (CQC) may be used to evaluate quantum radiation and fully treat the backreaction of quantum fields on classical backgrounds. The technique has widespread application, including to the quantum evaporation of classical breathers ("oscillons").