  Time-reversal symmetry and rotational invariance in spin space characterize
usual non-magnetic conductors. These symmetries give rise, at least, to
four-fold degenerate multiplets which, by definition, exhibit a null total
spin-momentum helicity. Thus, preventing a net spin transport. A proper choice
of geometry along with the intrinsic symmetry of the Bychkov-Rashba spin-orbit
interaction can be exploited to effectively reduce these two spin-related
symmetries to the timereversal one. It is shown that, in an ideal geometry, a
quantum dot with contacts having a specific geometry exhibit a single pair of
helical propagating states which makes this system ideal for pure spin current
generation. The strong quantization of the quantum dot's level structure would
make this mechanism robust against temperature effects.
