Optical Control of Spin Coherence in Singly Charged Quantum Dots

In singly charged dots, resonant light couples an electron in the ground state with a trion consisting of the electron and an excited electron-hole pair. We show that a polarized laser pulse, driving the electron/trion transition, coherently changes the spin state of the ground state electron. The controlled spin dynamics provide a mechanism for the optical orientation of an electron spin in a quantum dot. The theory is supported by experimental evidence of the electron spin coherence induced and controlled by optical pulses in (In,Ga)As/GaAs quantum dots.