  We study the propagation and storage of a quantum field using ultra-narrow
Coherent Population Oscillations (CPO) in a $\Lambda-$type atomic medium. The
predictions for classical fields are checked experimentally in a metastable
vapor at room temperature. We derive the evolution of its squeezing spectrum in
the presence of a large classical pump field which enables CPO to exist. We
show that the spontaneous emission of the residual population pumped into the
excited state progressively destroys the quantum noise properties of the
quantum field along propagation. The output quantum field therefore tends to be
a coherent state, discarding the possibility to store quantum states of light
with CPO.
