We study spin dynamics for two electrons confined to a double quantum dot under the influence of an oscillating exchange interaction. This leads to driven Rabi oscillations between the $\ket{ \uparrow\downarrow}$--state and the $\ket{ \downarrow\uparrow}$--state of the two--electron system. The width of the Rabi resonance is proportional to the amplitude of the oscillating exchange. A measurement of the Rabi resonance allows one to narrow the distribution of nuclear spin states and thereby to prolong the spin decoherence time. Further, we study decoherence of the two-electron states due to the hyperfine interaction and give requirements on the parameters of the system in order to initialize in the $\ket{ \uparrow\downarrow}$--state and to perform a $\sqrt{ \mathrm{ SWAP}}$ operation with unit fidelity.
Categories: cond-mat.mes-hall