  We propose a fast and accurate spin initialization method for a single
electron trapped in an electrostatic quantum dot. The dot is created in a
nanodevice composed of a catalytically grown indium antimonide (InSb) nanowire
and nearby gates to which control voltages are applied. Initially we insert a
single electron of arbitrary spin into the wire. Operations on spin are
performed using the Rashba spin-orbit interaction induced by an electric field.
First, a single pulse of voltages applied to lateral gates is used to split the
electron wavepacket into two parts with opposite spin orientations. Next,
another voltage pulse applied to the remaining gates rotates spins of both
parts in opposite directions by $\pi/2$. This way, initially opposite spin
parts eventually point in the same direction, along the axis of the quantum
wire. We thus set spin in a predefined direction regardless of its initial
orientation. This is achieved in time less than $60\,\mathrm{ps}$ without the
use of microwaves, photons or external magnetic fields.
