Ultrafast Spin Initialization in a Gated InSb Nanowire Quantum Dot

We propose a fast 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 wave packet into two parts with opposite spin orientations. Next, another voltage pulse applied to the remaining gates rotates the spins of both parts in opposite directions by pi/2. In 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 ps, without the use of microwaves, photons, or external magnetic fields.