Spin rotations induced by electron running on closed trajectories in   gated semiconductor nanodevices
  A design for a quantum gate performing transformations of a single electron spin is presented. The spin rotations are performed by the electron going around the closed loops in a gated semiconductor device. We demonstrate the operation of NOT, phase-flip and Hadamard quantum gates, i.e. the single-qubit gates which are most commonly used in the algorithms. The proposed devices employ the self-focusing effect for the electron wave packet interacting with the electron gas on the electrodes and the Rashba spin-orbit coupling. Due to the self-focusing effect the electron moves in a compact wave packet. The spin-orbit coupling translates the spatial motion of the electron into the rotations of the spin. The device does not require microwave radiation and operates using low constant voltages. It is therefore suitable for selective single-spin rotations in larger registers. 
S. Bednarek and B. Szafran