Cancellation of spin-orbit effects in quantum gates based on the exchange coupling in quantum dots.

We study the effect of the spin-orbit interaction on quantum gate operations based on the spin exchange coupling where the qubit is represented by the electron spin in a quantum dot or a similar nanostructure. Our main result is the exact cancellation of the spin-orbit effects in the sequence producing the quantum XOR gate for the ideal case where the pulse shapes of the exchange and spin-orbit interactions are identical. For the nonideal case, the two pulse shapes can be made almost identical and the gate error is strongly suppressed by two small parameters, the spin-orbit constant and the deviation of the two pulse shapes. We show that the dipole-dipole interaction leads only to very small errors in the XOR gate.