S. Varwig

Effect of pump-probe detuning on the Faraday rotation and ellipticity signals of mode-locked spins in (In,Ga)As/GaAs quantum dots

We have studied the Faraday rotation and ellipticity signals in ensembles of singly-charged (In,Ga)As/GaAs quantum dots by pump-probe spectroscopy. For degenerate pump and probe we observe that the Faraday rotation signal amplitude first grows with increasing the time separation between pump and probe before a decay is observed for large temporal separations. The temporal behavior of the ellipticity signal, on the other hand, is regular: its amplitude decays with the separation. By contrast, for detuned pump and probe the Faraday rotation and ellipticty signals both exhibit similar and conventional behavior. The experimental results are well described in the frame of a recently developed microscopic theory [Phys. Rev. B 80, 104436 (2009)]. The comparison between calculations and experimental data allows us to provide insight into the spectral dependence of the electron spin precession frequencies and extract the electron g-factor dependence on energy.

Temperature dependence of hole spin coherence in (In,Ga)As quantum dots measured by mode-locking and echo techniques

The temperature dependence of the coherence time of hole spins confined in self-assembled (In,Ga)As/GaAs quantum dots is studied by spin mode-locking and spin echo techniques. Coherence times limited to about a \mu s are measured for temperatures below 8 K. For higher temperatures a fast drop occurs down to a few ns over a 10 K range. The hole-nuclear hyperfine interaction appears too weak to account for these limitations. We suggest that spin-orbit related interactions are the decisive sources for hole spin decoherence.

Dispersion of electron g-factor with optical transition energy in (In,Ga)As/GaAs self-assembled quantum dots

The electron spin precession about an external magnetic field was studied by Faraday rotation on an inhomogeneous ensemble of singly charged, self-assembled (In,Ga)As/GaAs quantum dots. From the data the dependence of electron g-factor on optical transition energy was derived. A comparison with literature reports shows that the electron g-factors are quite similar for quantum dots with very different geometrical parameters, and their change with transition energy is almost identical.

Optical Control of Coherent Interactions between Electron Spins in InGaAs Quantum Dots

S. Spatzek, A.Greilich, SophiaE.Economou, S. Varwig, A. Schwan, D.R.Yakovlev, D.Reuter, A.D.Wieck, T. L.Reinecke, and M.Bayer Experimentelle Physik 2, Technische Universität Dortmund, D-44221 Dortmund, Germany Naval Research Laboratory, Washington, D.C. 20375, USA A. F. Ioffe Physico-Technical Institute, RAS, St. Petersburg, 194021 Russia and Angewandte Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany (Dated: October 3, 2011)

Generation and detection of mode-locked spin coherence in (In,Ga)As/GaAs quantum dots by laser pulses of long duration

Using optical pulses of variable duration up to 80 ps, we report on spin coherence initialization and its subsequent detection in n-type singly-charged quantum dots, subject to a transverse magnetic field, by pump-probe techniques. We demonstrate experimentally and theoretically that the spin coherence generation and readout efficiencies are determined by the ratio of laser pulse duration to spin precession period: An increasing magnetic field suppresses the spin coherence signals for a fixed duration of pump and/or probe pulses, and this suppression occurs for smaller fields the longer the pulse duration is. The reason for suppression is the varying spin orientation due to precession during pulse action.

All-optical implementation of a dynamic decoupling protocol for hole spins in (In,Ga)As quantum dots

(Received 9 May 2014; revised manuscript received 15 September 2014; published 30 September 2014)We demonstrate the potential of a periodic laser-pulse protocol for dynamic decoupling of hole spins in(In,Ga)As quantum dots from surrounding baths. When doubling the repetition rate of inversion laser pulsesbetweentworeferencepulsesfororientingthespins,wefindthatthespincoherencetimeisincreasedbyafactorof 2.DOI: 10.1103/PhysRevB.90.121306 PACS number(s): 76

Non-resonant optical excitation of mode-locked electron spin coherence in (In,Ga)As/GaAs quantum dot ensemble

Two-color pump probe experiments reveal the possibility to use non-resonant pulsed laser excitation to create mode-locking of the ground state electron spin precessions in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. The mode-locking shows a resonance for excitation into the first excited shell while for excitation into higher shells or barriers it disappears; however, spin coherence can still be induced. We conclude that the optically excited carriers relax spin-conserved from the p-shell into their ground states on a picosecond time scale, much shorter than the spin revolution period about the magnetic field.