  Detection schemes for the quantum chromodynamics axions and other axion-like
particles in light-shining-through-a-wall (LSW) experiments are based on the
conversion of these particles into photons in a magnetic field. An alternative
scheme may involve the detection via a resonant atomic or molecular transition
induced by resonant axion absorption. The signal obtained in this process is
second order in the axion-electron interaction constant but may become first
order if we allow interference between the axion-induced transition amplitude
and the transition amplitude induced by the electromagnetic radiation that
produces the axions.
