Resonant two-color high-resolution spectroscopy of a negatively charged exciton in a self-assembled quantum dot

We report high-resolution resonant two-color laser spectroscopy on single self-assembled InGaAs quantum dots. The negatively charged exciton in a quantum dot can decay radiatively into both electron-spin ground states, the states with an electron in the quantum dot with its spin parallel or antiparallel to an applied magnetic field. The two decay paths can be used for optical spin alignment via optical pumping. We apply two laser fields at two different colors resonant with the two Zeeman split optical transitions to study the properties of the spin of the resident electron in the quantum dot in both the Faraday and Voigt geometries. The resonant two-color signal is monitored as a function of the laser power as well as the applied magnetic and electric field allowing us to determine spin decay and dephasing rates. We find the rate at which the optical spin alignment can be performed depending on the direction and the magnitude of the applied magnetic field. Finally we demonstrate the feasibility of performing coherent all-optical spin manipulation of an electron spin in a quantum dot. © 2008 The American Physical Society.