  An electron within a mesoscopic (quantum-coherent) spintronic structure is
described by a single wave function which, in the presence of both charge
scattering and spin-orbit coupling, encodes an information about {\em
entanglement} of its spin and orbital degrees of freedom. The quantum state--an
{\em improper} mixture--of experimentally detectable spin subsystem is
elucidated by evaluating quantum information theory measures of entanglement in
the scattering states which determine {\em quantum transport} properties of
spin-polarized electrons injected into a two-dimensional disordered Rashba
spin-split conductor that is attached to the ferromagnetic source and drain
electrodes. Thus, the Landauer transmission matrix, traditionally evaluated to
obtain the spin-resolved conductances, also yields the reduced spin density
operator allowing us to extract quantum-mechanical measures of the detected
electron spin-polarization and spin-coherence, thereby pointing out how to
avoid detrimental {\em decoherence} effects on spin-encoded information
transport through semiconductor spintronic devices.
