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Physical Review Letters

Coherent Spectroscopy of Optically Gated Charged Single InGaAs Quantum Dots

Lucien Besombes, J.J. Baumberg, Junichi Motohisa

Published Jun 25, 2003• 93 citations
Publisher

Abstract

The excited states of neutral and charged single InGaAs/GaAs quantum dots are studied using a confocal microspectroscopy technique. Because of their different Coulomb energy shifts, the charged and neutral states of the same quantum dot can be selectively excited. The charge of the quantum dot is controlled by a photo-depletion mechanism. Time-resolved coherent spectroscopy shows that the dephasing time of the excited states is longer when the quantum dot is charged. Rabi oscillation of the excited state of a singly charged quantum dot is demonstrated.

DOI
10.1103/physrevlett.90.257402

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We present measurements of the dephasing time and of optical Rabi oscillations in the excitonic ground-state transition of an InGaAs quantum dot ensemble at low temperature, using an heterodyne pump–probe technique. Dephasing times of several hundred picoseconds are measured, enabling coherent light–matter interaction with picosecond optical pulses. Optical Rabi oscillations which are damped versus pulse area and change period when changing pulse duration are observed. Comparison with calculations indicates that the observed damping is not intrinsic to a single dot. Dephasing processes and the biexciton resonance change the amplitude and the period of the oscillations, respectively, while the damping versus pulse area is due to a distribution of transition dipole moments in the ensemble.
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Optical Rabi oscillations are coherent population oscillations of a two-level system coupled by an electric dipole transition when driven by a strong nearly resonant optical field. In quantum dot structures, these measurements have typically been performed as a function of the total pulse area $\ensuremath{\int}{\ensuremath{\Omega}}_{0}(t)\phantom{\rule{0.16em}{0ex}}\mathrm{d}t$ where the pulse area varies as a function of Rabi frequency. Here, we report direct detection of the time-resolved coherent transient response of the resonance fluorescence to measure the time evolution of the optical Rabi oscillations in a single charged InAs quantum dot. We extract a decoherence rate consistent with the limit from the excited state lifetime.