Optical control of spin coherence in singly charged (In,Ga)As/GaAs   quantum dots
  Electron spin coherence has been generated optically in n-type modulation doped (In,Ga)As/GaAs quantum dots (QDs) which contain on average a single electron per dot. The coherence arises from resonant excitation of the QDs by circularly-polarized laser pulses, creating a coherent superposition of an electron and a trion state. Time dependent Faraday rotation is used to probe the spin precession of the optically oriented electrons about a transverse magnetic field. Spin coherence generation can be controlled by pulse intensity, being most efficient for (2n+1)pi-pulses. 
A. Greilich (1), R. Oulton (1), E. A. Zhukov (1), I. A. Yugova (1), D.   R. Yakovlev (1 and 3), M. Bayer (1), A. Shabaev (2)...