Optically driven qubits in artificial molecules

We present 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 a monochromatic light pulse illuminated on the quantum dots. Considering particular types of artificial molecules, we show that the qubit is easily manipulated with the polarization and frequency of a light pulse and, especially, the controlled-NOT operation can be possible exploiting the electron-electron interaction. To examine the decoherence of quantum states, we discuss electronic relaxation contributed mainly by LA phonon processes.