An ultrashort half-cycle pulse ͑HCP͒ is a fast (Ͻ1 ps) unipolar pulse, followed by a much longer (ϳ100 ps) and weaker unipolar pulse of opposite polarity. We show that such pulses can be utilized to localize, within femtoseconds, and control, for picoseconds, the electronic motion in a Al x Ga 1Ϫx As based symmetric double quantum well. The results are obtained by (i) deriving analytically for a model system the type of HCPs that lead to a fast and sustainable localization of a desirable final electron state and (ii) by solving numerically exactly the time-dependent Schrödinger equation for the quantum-well structure in the presence of the HCPs.