  Without access to the full quantum state, modeling quantum transport in
mesoscopic systems requires dealing with a limited number of degrees of
freedom. In this work, we analyze the possibility of modeling the perturbation
induced by the non-simulated degrees of freedom on the simulated ones as a
transition between single-particle pure states. First, we show that Bohmian
conditional wave functions (BCWF) allow a rigorous discussion of the dynamics
of electrons inside open quantum systems in terms of such single-particle pure
states, either under Markovian or non-Markovian conditions. Second, we discuss
the practical application of the method for modeling light-matter interaction
phenomena in a resonant tunneling device (RTD), where a single photon is
interacting with a single electron. Third, we emphasize the importance of
interpreting such scattering mechanism as a transition between initial and
final single-particle BCWF with well-defined energies (rather than with
well-defined momenta).
