Electrical control of spin coherence in semiconductor nanostructures

The processing of quantum information based on the electron spin degree of freedom(1,2) requires fast and coherent manipulation of local spins. One ap proach is to provide spatially selective tuning of the spin splitting-which depends on the g-factor-by using magnetic fields(3), but this requires the ir precise control at reduced length scales. Alternative proposals employ e lectrical gating(1) and spin engineering in semiconductor heterostructures involving materials with different g-factors. Here we show that spin cohere nce can be controlled in a specially designed AlxGa1-xAs quantum well in wh ich the Al concentration x is gradually varied across the structure. Applic ation of an electric field leads to a displacement of the electron wavefunc tion within the quantum well, and because the electron g-factor varies stro ngly with x, the spin splitting is therefore also changed. Using time-resol ved optical techniques, we demonstrate gate-voltage-mediated control of coh erent spin precession over a 13-GHz frequency range in a fixed magnetic fie ld of 6 T, including complete suppression of precession, reversal of the si gn of g, and operation up to room temperature.