Picosecond coherent optical manipulation of a single electron spin in a quantum dot

Most schemes for quantum information processing require fast single- qubit operations. For spin-based qubits, this involves performing arbitrary coherent rotations of the spin state on time scales much faster than the spin coherence time. By applying off- resonant, picosecond- scale optical pulses, we demonstrated the coherent rotation of a single electron spin through arbitrary angles up to p radians. We directly observed this spin manipulation using time- resolved Kerr rotation spectroscopy and found that the results are well described by a model that includes the electron-nuclear spin interaction. Measurements of the spin rotation as a function of laser detuning and intensity confirmed that the optical Stark effect is the operative mechanism.