Regensburg 2007 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 12: Quantum dots and wires: Optical properties I
HL 12.2: Talk
Monday, March 26, 2007, 15:00–15:15, H17
Mode locking of electron spin coherences in singly charged InGaAs/GaAs quantum dots — •Alex Greilich1, Dmitri Yakovlev1, Andrew Shabaev2, Alexander Efros2, Irina Yugova1, Ruth Oulton1, Victorina Stavarache3, Dirk Reuter3, Andreas Wieck3, and Manfred Bayer1 — 1Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany — 2Naval Research Laboratory, Washington, DC 20375, USA — 3Angewandte Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
We report an optical technique based on time-resolved Faraday rotation measurements of the electron spin dynamics in an ensemble of QDs to recover the coherence time of a single QD. The measured spin coherence time T2 is 3 microseconds, which is three orders of magnitude longer than the ensemble dephasing time of about 2 nanoseconds. A periodic train of circularly polarized light pulses from a mode-locked laser synchronizes the precession of the spins to the laser repetition rate TR, transferring the mode-locking into the spin system. This synchronization leads to constructive interference of the electron spin polarization in time. The interference gives also the possibility for all-optical coherent manipulation of spin ensembles: the electron spins can be clocked by two trains of pump pulses with a fixed temporal delay TD. After this pulse sequence, the QD ensemble shows multiple echo-like Faraday rotation signals with a period equal to the pump pulse separation.