Electrically driven single spin resonance in double quantum dots

We report on our recent progress in applying semiconductor quantum dots to quantum information processing with electron spin qubits. Mixing the electron's spin and charge degrees of freedom via a magnetic field gradient enables reasonably fast single spin rotations driven by electric fields. We generate sufficiently strong gradients on-chip using micron-size ferromagnets. Our method bypasses the need for localized and strong microwave magnetic fields, which in comparison are difficult to apply in quantum dots. In addition, micro-magnets facilitate the selective manipulation of electron spins. We demonstrate proper operation of our micro-magnet approach using GaAs double quantum dots where single spin resonances and coherent rotations are observed. Preliminary results on combining 1 and 2-qubits operations are also presented. The strong nuclear spin fluctuations in the GaAs lattice cause fast decoherence and limit the quality factor of electron spin qubits. On-going efforts to solve the decoherence problem use material free of nuclear spins (e.g. isotopically purified SiGe). Although the other leading electric coupling mechanism, the spin-orbit interaction, work well in GaAs, it might not be as efficient in these materials. Our micro-magnet method - which is applicable to any material - is therefore a crucial component for the further development of electron spin qubits in quantum dots. Moreover, the micro-magnet design we present has applications to other kind of spin qubits like paramagnetic defects in silicon.