  Transporting ensembles of electrons over long distances without losing their
spin polarization is an important benchmark for spintronic devices. It requires
usually to inject and to probe spin polarized electrons in conduction channels
using ferromagnetic contacts or optical excitation. Parallel to this
development, an important effort has been dedicated to the control of
nanocircuits at the single electron level. The detection and the coherent
manipulation of the spin of a single electron trapped in a quantum dot are now
well established. Combined with the recent control of the displacement of
individual electrons between two distant quantum dots, these achievements
permit to envision the realization of spintronic protocols at the single
electron level. Here, we demonstrate that spin information carried by one or
two electrons can be transferred between two quantum dots separated by a
distance of 4 micrometers with a classical fidelity of 65 %. We show that it is
presently limited by spin flips occurring during the transfer procedure prior
to and after the electron displacement. Being able to encode and control
information in the spin degree of freedom of a single electron while being
transferred over distances of a few microns on nanosecond timescales paves the
way towards "quantum spintronics" devices where large scale spin-based quantum
information processing could be implemented.
