  We explore a possibility of measuring the magnitude and the Majorana nature
of neutrino masses, by using a novel process of neutrino pair emission from
excited atoms. Except lepton number non-conserving processes, the neutrino pair
($\nu \bar{\nu}$) emission is the unique process to distinguish the Majorana
neutrino from the Dirac neutrino. The small energy difference between atomic
levels makes it easier to measure small neutrino masses as indicated by
neutrino oscillation experiments. The crucial point is how to enhance the rate
of pair emission without enhancing the radiative decay. We have in mind two
particular cases; (1) laser irradiated pair emission from metastable atoms, and
(2) microwave irradiated emission from circular Rydberg states. A new mechanism
of the parametric amplification to enhance the neutrino pair emission is
pointed out when Rydberg atoms are irradiated by microwave, while the radiative
process may be inhibited by the cavity QED effect. A great variety of
measurable neutrino parameters and a variety of experimental methods are
conceivable.
