Electrical preparation and readout of a single spin state in a quantum dot via spin bias

Based on the device in recent experiments [S. M. Frolov et al., Phys. Rev. Lett. 102, 116802 (2009); Nature (London) 458, 868 (2009)], we propose an all-electrical scheme to prepare and readout a single spin state in a quantum dot (QD). We consider that the QD, which is subjected to a spin bias, has a single spin-degenerate energy level _d in the presence of Coulomb interaction U. By tuning the energy level controlled experimentally by a gate voltage, write in and read out the spin information can be achieved in the following way. When the level _d is within the spin bias window, a spin state can be written into the dot even for very weak spin bias. When both _d and _d+U are tuned to be out of the spin bias window, the initialized spin state can be preserved on the dot for a very long time (e.g., on the order of second), during which many qubit manipulations can be accomplished. Finally, by tuning the level _d+U to the spin bias window, the spin state can be read out by measuring the charge current. ©2010 The American Physical Society