  We study the dynamics of an electron weakly coupled to a phonon gas. The
initial state of the electron is the superposition of two spatially localized
distant bumps moving towards each other, and the phonons are in a thermal
state. We investigate the dynamics of the system in the kinetic regime and show
that the time evolution makes the non-diagonal terms of the density matrix of
the electron decay, destroying the interference between the two bumps. We show
that such a damping effect is exponential in time, and the related decay rate
is proportional to the total scattering cross section of the electron-phonon
interaction.
