Controlled exchange interaction for quantum logic operations with spin qubits in coupled quantum dots

A two-electron system confined in two coupled semiconductor quantum dots is investigated as a candidate for performing quantum logic operations on spin qubits. We study different processes of swapping the electron spins by controlled switching on/off the exchange interaction. The resulting spin swap corresponds to an elementary operation in quantum information processing. We perform a direct time evolution simulations of the time-dependent Schroedinger equation. Our results show that -- in order to obtain the full interchange of spins -- the exchange interaction should change smoothly in time. The presence of jumps and spikes in the corresponding time characteristics leads to a considerable increase of the spin swap time. We propose several mechanisms to modify the exchange interaction by changing the confinement potential profile and discuss their advantages and disadvantages.