Macro-coherent two photon and radiative neutrino pair emission

We discuss a possibility of detecting a coherent photon pair emission and related radiative neutrino pair emission from excited atoms. It is shown that atoms of lambda- and ladder-type three level system placed in a pencil-like cylinder give a back to back emission of two photons of equal energy $\mathrm{\Delta }\mathrm{/}2$, sharply peaked with a width $\propto$ 1/(target size) and well collimated along the cylinder axis. This process has a measurable rate $\propto$ (target number density) ${}^2\times$ target volume, while a broader spectral feature of one-photon distribution separated by (mass sum of a neutrino pair)${}^2\mathrm{/}(2\mathrm{\Delta })$ from the two photon peak may arise from radiative neutrino pair emission, with a much smaller rate.