  Coherent single-electron control in a realistic semiconductor double quantum
dot is studied theoretically. Using optimal-control theory we show that the
energy spectrum of a two-dimensional double quantum dot has a fully
controllable transition line. We find that optimized picosecond laser pulses
generate population transfer at significantly higher fidelities (>0.99) than
conventional sinusoidal pulses. Finally we design a robust and fast charge
switch driven by optimal pulses that are within reach of terahertz laser
technology.
