  We discuss a dynamical mechanism of pion production from disoriented chiral
condensates (DCC). It leads to an explosive production of pions via the
parametric amplification mechanism, which is similar to the reheating mechanism
in inflationary cosmology. Classically, it is related with the instability in
the solutions of the Mathieu equation and we explore the quantum aspects of the
mechanism. We show that nonlinearlities and back reactions can be ignorable for
sufficiently long time under the small amplitude approximations of background
$\sigma$ oscillations, which may be appropriate for the late stage of
nonequilibrium phase transition. It allows us to obtain an explicit quantum
state of the produced pions and $\sigma$, the squeezed state of BCS type.
Single particle distributions and two-pion correlation functions are computed
within these approximations. The results obtained illuminate the characteristic
features of multi-pion states produced through the parametric amplification
mechanism. In particular, two-pion correlations of various charge combinations
contain back-to-back correlations which cannot be masked by the identical
particle interference effect.
