  Electron transport properties in a parallel double-quantum-dot structure with
three-terminals are theoretically studied. By introducing a local Rashba
spin-orbit coupling, we find that an incident electron from one terminal can
select a specific terminal to depart from the quantum dots according to its
spin state. As a result, spin polarization and spin separation can be
simultaneously realized in this structure. And spin polarizations in different
terminals can be inverted by tuning the structure parameters. The underlying
quantum interference that gives rise to such a result is analyzed in the
language of Feynman paths for the electron transmission.
