  A rigorous microscopic theory for the description of quantum-transport
phenomena in systems with open boundaries is proposed. We shall show that the
application of the conventional Wigner-function formalism to this problem leads
to unphysical results, like injection of coherent electronic states from the
contacts. To overcome such basic limitation, we propose a generalization of the
standard Wigner-function formulation, able to properly describe the incoherent
nature of carrier injection at the device spatial boundaries as well as the
interplay between phase coherence and energy relaxation/dephasing within the
device active region. The proposed theoretical scheme constitutes the first
rigorous derivation of the phenomenological injection model commonly employed
in the simulation of open quantum devices.
