  We present novel models of quantum gates based on coupled quantum dots in
which a qubit is regarded as the superposition of ground states in each dot.
Coherent control on the qubit is performed by both a frequency and a
polarization of a monochromatic light pulse illuminated on the quantum dots. We
also show that a simple combination of two single qubit gates functions as a
controlled NOT gate resulting from an electron-electron interaction. To examine
the decoherence of quantum states, we discuss electronic relaxation contributed
mainly by LA phonon processes.
