Control and measurement of electron spins in semiconductor quantum dots

We present an overview of experimental steps taken towards using the spin of a single electron trapped in a semiconductor quantum dot as a spin qubit [Loss and DiVincenzo, Phys. Rev. A 57, 120 (1998)]. Fabrication and characterization of a double quantum dot containing two coupled spins has been achieved, as well as initialization and single-shot read-out of the spin state. The relaxation time T-1 of single-spin and two-spin states was found to be on the order of a millisecond, dominated by spin-orbit interactions. The time-averaged dephasing time T*, due to fluctuations in the ensemble of nuclear spins in the host semi-conductor, was determined to be on the order of several tens of nanosceconds. Coherent manipulation of single-spin states can be performed using a microfabricated wire located close to the quantum dot, while two-spin interactions rely on controlling the tunnel barrier connecting the respective quantum dots [Petta et al., Science 309, 2180 (2005)]. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.