  We present detailed simulations addressing recent electronic interference
experiments, where a metallic gate is used to locally modify the Fermi
wave-length of the charge carriers. Our numerical calculations are based on a
solution of the one-particle Schroedinger equation for a realistic model of the
actual sample geometry, including a Poisson equation based determination of the
potential due to the gate. The conductance is determined with the multiprobe
Landauer-Buettiker formula, and in general we find conductance vs. gate voltage
characteristics which closely resemble the experimental traces. A detailed
examination based on quantum mechanical streamlines suggests that the simple
one-dimensional semiclassical model often used to describe the experiments has
only a limited range of validity, and that certain 'unexpected' periodicities
should not be assigned any particular significance, they arise due to the
complicated multiple scattering processes occurring in certain sample
geometries.
