Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 44: Semiconductor Microcavities and Entangled States in Quantum Dots

HL 44.1: Invited Talk

Thursday, March 29, 2007, 14:00–14:30, H15

Electron spin dynamics in quantum dots — •Manfred Bayer — Experimentelle Physik II, Universität Dortmund, D-44221 Dortmund, Germany

Electron spins in quantum dots (QDs) are promising candidates to serve as building blocks for semiconductor based quantum information technologies. Due to the unavoidable inhomogeneities in a QD ensemble it is common believe that coherent manipulations need to be performed on a single dot level. In this contribution we will show that by proper addressing of QDs by pulsed laser protocols it might be possible to perform corresponding studies on QD ensembles, with all the related benefits such as strong spectroscopic response.

For our experiments we have primarily used a time-resolved Faraday rotation technique on (In,Ga)As/GaAs quantum dots single charged with on electron. Using this methodology we will show: (i) trains of circularly polarized laser pulses are extremely efficient to create spin coherence (spin initialization) [1]. (ii) Such pulse trains can be used to synchronize certain spin subsets within the ensemble. From the dependence of the synchronization on the pulse separation the electron spin coherence time can be measured to be 3 µs at cryogenic temperatures [2]. (iii) The spins can be clocked by pulse doublet sequences such that they show periodic coherent responses. The period of these responses can be tailored by the details of the laser excitation [3].

Finally we will also address the impact of the interaction of the electron spins with the background of nuclei, which is considered to be one of the prime reasons for spin dephasing. We will show that under specific conditions a strong interaction between electron and nuclear spins will be established leading to a drastic enhancement of the spin relaxation time.

[1] A. Greilich, R. Oulton, E. A. Zhukov, I. A. Yugova, D. R. Yakovlev, M. Bayer, A. Shabaev, Al. L. Efros, I. A. Merkulov, V. Stavarache, D. Reuter, and A. Wieck, Phys. Rev. Lett. 96, 227401 (2006).

[2] 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).

[3] A. Greilich, M. Wiemann, F.G.G. Hernandez, D.R. Yakovlev, I.A. Yugova, M. Bayer, A. Shabaev, Al.L. Efros, D. Reuter and A.D. Wieck, submitted for publication.

[4] R. Oulton, A. Greilich, S. Yu. Verbin, R. V. Cherbunin, T. Auer, D.R.Yakovlev, M. Bayer, I. A. Merkulov, V. Stavarache, D. Reuter, and A. D. Wieck, submitted for publication.