Zeno and anti-Zeno effects in multimode parametric down-conversion

We present a simple multimode analysis of the Zeno and anti-Zeno effects in spontaneous parametric down-conversion. In this process the input vacuum is an unstable state decaying into a reservoir of down-converted modes by emitting a pair of photons. We show that the Zeno and the anti-Zeno effects are two particular examples of quantum propagation depending on the effective spectrum of down-converted modes. We show that this evolution can be easily tailored on demand and that these quantum phenomena admit a very simple explanation in terms of standard interference concepts