  Real time quantum dynamics of the spontaneous translational symmetry breakage
in the early stage of photoinduced structural phase transitions is reviewed and
supplementally explained, under the guide of the Toyozawa theory, which is
exactly in compliance with the conservation laws of the total momentum and
energy. At the Franck Condon state, an electronic excitation just created by a
visible light, is in a plane wave state, extended all over the crystal. While,
after the lattice relaxation having been completed, it is localized around a
certain lattice site of the crystal, as a new excitation. Is there a sudden
shrinkage of the excitation wave function, in between. The wave function never
shrinks, but only the spatial, or inter lattice site quantum coherence,
interference of the excitation disappears, as the lattice relaxation proceeds.
This is nothing but the spontaneous breakage of translational symmetry.
