All optical quantum dot spin manipulation

The coherence time of an excess electron spin confined in a quantum dot structure is expected to be orders of magnitude longer than the typical timescales required for its coherent manipulation. Motivated by this observation, several groups have proposed to use single quantum dot spins as quantum bits (qubits), and to manipulate, couple and measure individual spins using either transport or optical techniques. In the case of quantum dots with stronger confinement along the growth direction, lowest energy elementary optical transitions are those arising from excitation of a m_z=3/2 (m_z=-3/2) valence band electron to a m_z=1/2 (m_z=-1/2) conduction band state. If the quantum dot already has an excess conduction band electron, only one of these optical (trion) transitions is allowed; the other is spin (Pauli) blocked, in contrast, a neutral quantum dot always has a pair of exciton excitations. It has been suggested that Pauli blocking of absorption or fluorescence can be used to implement high efficiency all-optical single-spin measurements and conditional spin dynamics. In this talk, we will review our work aimed at experimental demonstration of Pauli blocking and single-spin measurement in single-electron-charged self-assembled quantum dots.