Berlin 2008 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 16: Quantum dots and wires: Optical properties I

HL 16.3: Talk

Monday, February 25, 2008, 14:30–14:45, ER 164

Tailoring of mode-locking by shaping laser pulse sequencies — •Stefan Spatzek, Alex Greilich, Dmitri Yakovlev, and Manfred Bayer — Experimentelle Physik II, Technische Universität Dortmund, D-44221 Dortmund, Germany

Electron spins in ensembles of quantum dots (QDs) provide an attractive proposal to implement quantum information technologies in a solid-state environment. Unfortunately, inhomogeneities within an ensemble lead to the rapid loss of coherence among the phases of the spins.

We report about the mode-locking effect on InGaAs/GaAs QDs, dependent on the temporal pulsewidth at different magnetic fields in a range of 150 - 800 fs measured by time-resolved Faraday rotation. A periodic train of circularly polarized light pulses of mode-locked laser synchronizes the precession of the spins to the laser repetition rate, transferring the mode-locking into the spin system [1]. We have proved, that the mode-locking effect is more pronounced by longer excitation pulses, due to decreasing of the spectral width of the pulse. In the excited inhomogeneous QDs ensemble one observes the spin precessions on different frequencies. Therefore, with decreasing of the spectral pulsewidth one excites smaller distribution of the QDs, that lead to the longer dephasing of the QD ensamble.

[1] A. Greilich, D. R. Yakovlev, A. Shabaev, Al. L. Efros, I. A. Yugova, R. Oulton, V. Stavarache, D. Reuter, A. Wieck, and M. Bayer, Science 313, 341 (2006).