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 entanglement of its spin and orbital degrees of freedom. The quantum state—an improper mixture—of experimentally detectable spin subsystem is elucidated by evaluating quantum information theory measures of entanglement in the scattering states which determine 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 decoherence effects on spin-encoded information transport through semiconductor spintronic devices.