  A numerical-analytical simulation of scattering by a three-barrier
heterostructure of an electronic Gaussian wave packet, the spectral width of
which is on the order of the distance between the levels of the doublet of
quasi-stationary states, is carried out. It is shown that as a result of
scattering, damped waves of electron charge and current densities are formed
outside the double well, their characteristics are determined by the structure
of the initial wave packet and the poles of the scattering amplitudes. The
frequency of these waves is equal to the difference frequency of the doublet,
the wavenumber is the difference between the wave numbers of free motion of
electrons with resonant energies, and the speed of their propagation is the
ratio of these quantities. The system can go into the regime of repetition or
amplification of the emission of electron waves if a periodic resonant pumping
of the doublet population is provided by scattering of a series of coherent
wave packets.
