Ultrafast optical control of electron spin coherence in chargedGaAsquantum dots

Impulsive stimulated Raman excitation with coherent optical fields is used for controlling the electron spin coherence in a charged $\mathrm{GaAs}$ quantum dot ensemble through an intermediate charged exciton (trion) state. The interference between two stimulated Raman two-photon quantum mechanical pathways leading to the spin coherence allows us to control the electron spin coherence on the time scale of the Larmor precession frequency. We also demonstrate, both theoretically and experimentally, that ultrafast manipulation of the spin coherence is possible on the time scale of the optical laser frequency, and analyze the limitations due to the trion and spin decoherence times.