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Physica status solidi. C, Conferences and critical reviews/Physica status solidi. C, Current topics in solid state physics

Observation of an unusual temperature dependence of the initial decoherence time in quantum dots

V. M. Axt, T. Kühn, Alexei Vagov, Paola Borri, W. Langbein, U. Woggon

Published May 1, 2005• 0 citations
Publisher

Abstract

We report on four-wave-mixing experiments in self-assembled InAs/GaAs quantum dots and compare with a theory that accounts for the pure-dephasing induced by acoustic phonons. The measurements demonstrate an unusual non-monotonous temperature dependence of the initial decoherence time in full agreement with previous theoretical predictions made on the basis of a model that concentrates on the lowest electronic states. For samples exhibiting strong electronic confinement this model even yields a good quantitative agreement with the experiments while for less confined samples there are some systematic deviations although many qualitative features are still well reproduced by the model. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI
10.1002/pssc.200460779

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physica status solidi (b)•Jul 12, 2006•2 citations
We report on four-wave-mixing experiments in self-assembled InAs/GaAs quantum dots and compare with a theory that accounts for the pure-dephasing induced by acoustic phonons. The measurements demonstrate an unusual non-monotonous temperature dependence of the initial decoherence time in full agreement with previous theoretical predictions made on the basis of a model that concentrates on the lowest electronic states. For samples exhibiting strong electronic confinement this model even yields a good quantitative agreement with the experiments while for less confined samples there are some systematic deviations although many qualitative features are still well reproduced by the model. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Abstract The impact of pure dephasing processes on the optically induced nonlinear dynamics of quantum dots is analyzed. Concentrating on small dots pure dephasing can be studied analytically in the limit of ultrafast excitation. General conclusions from the analysis of the closed form formulas include the prediction that four‐wave‐mixing (FWM) spectra of single dots change from asymmetric to symmetric lineshapes with increasing pulse delay. Furthermore, in contrast to phenomenological dephasing models the delay dependence of the time integrated FWM amplitude |PFWM| generated by a strongly inhomogeneously broadened ensemble deviates from the real time dependence of |Plin|2, where Plin is the linear polarization emitted by a single dot. Numerical results are presented for FWM signals from dots coupled to bulk acoustic phonons. Surprisingly, the initial decay time of the signal depends non‐monotonously on the temperature. In addition, it is shown that for certain material parameters the coupling to the smooth continuum of acoustic phonons may result in pronounced oscillations.
We have performed time-integrated degenerate four-wave mixing experiments in InAs/GaAs self-assembled quantum dots. The quantum dots are excited in resonance with an intersublevel transition between the valence states of the dots. The dephasing time T2{T}_{2}T2​ is deduced from the time dependence of the photon echo amplitude as a function of the delay between the two incident pulses. At low temperature, a dephasing time T2{T}_{2}T2​ of 15 ps is measured for a resonant excitation at 7.4 \ensuremath{\mu}m wavelength. This dephasing corresponds to an homogeneous broadening of the intersublevel transition of 87 \ensuremath{\mu}eV. The polarization decay time is much longer than the one observed for resonant intersubband excitations in quantum wells. The dephasing time of the intersublevel polarization exhibits only a weak temperature dependence, indicating that the dephasing is not dominated by phonon-assisted scattering mechanisms.