Entanglement of Electron Spin and Orbital States in Spintronic Quantum Transport

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.