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Journal of Modern Optics

Many-body theory of quantum coherence in semiconductor quantum dots

Chi‐Wai Chow, S. Michael, Hans Christian Schneider

Published Nov 10, 2007• 15 citations
Publisher

Abstract

A many-body theory for quantum coherence in a semiconductor quantum-dot system is presented. We present the theory in detail for a Λ scheme in a InGaAs–GaAs quantum dot with a pulsed drive field. The paper shows the significant differences in the predictions of this theory and those of an independent-particle treatment, adapted from atomic quantum coherence theory. Specifically, the influence of the quantum-dot level structure on group-velocity slowdown is discussed, and the influence of different Coulomb renormalization effects is analysed.

DOI
10.1080/09500340701639664

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arXiv:1403.4790•Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Mar 7, 2014•2 citations
A many-body theory for quantum coherence in a semiconductor quantum-dot system is presented. We present the theory in detail for a Λ scheme in a InGaAs–GaAs quantum dot with a pulsed drive field. The paper shows the significant differences in the predictions of this theory and those of an independent-particle treatment, adapted from atomic quantum coherence theory. Specifically, the influence of the quantum-dot level structure on group-velocity slowdown is discussed, and the influence of different Coulomb renormalization effects is analysed.
Quantum-coherence induced group-velocity slowdown in a semiconductor quantum-dot structure is investigated using a many-body theory. The predictions are found to be noticeably different from those obtained in the independent-particle treatment typically used for describing atomic quantum coherence. In particular, Hartree-Fock renormalizations can lead to over two orders of magnitude reduction in the predicted pump intensity requirement for group-velocity slowdown to occur. Results are presented for the slowdown factor and slowdown-bandwidth product in a pulsed InAs–GaAs quantum-dot Λ scheme.
In this paper, the many-body aspects and the differences to the independent-particle treatment of quantum coherence in QDs are discussed. For investigation the semiconductor Bloch equations, modified for a Lambda system, is used. A relatively detailed description of the electronic states of a coupled QD-QW system and the coupling of these states via collisions in the relaxation rate approximation is included. A structure consisting of InAs pyramidal dots with a base of 12 x 12 nm and height 6 nm on a wetting layer of thickness 1 nm embedded in a GaAs QW is chosen for the study. Here, the slow-down factor S, which is a measure of the refractive index changes resulting in optical group-velocity reduction and thus of interest for applications such as optical storage, is focused.
This paper explores quantum-coherence phenomena in a semiconductor quantum-dot structure. The calculations predict the occurrence of inversionless gain, electromagnetically induced transparency, and refractive-index enhancement in the transient regime for dephasing rates typical under room temperature and high excitation conditions. They also indicate deviations from atomic systems because of strong many-body effects. Specifically, Coulomb interaction involving states of the quantum dots and the continuum belonging to the surrounding quantum well leads to collision-induced population redistribution and many-body energy and field renormalizations that modify the magnitude, spectral shape, and time dependence of quantum-coherence effects.
The slowdown of optical pulses due to quantum-coherence effects is investigated theoretically for an ``active material'' consisting of InGaAs-based double quantum dot molecules. These are designed to exhibit a long-lived coherence between two electronic levels, which is an essential part of a quantum-coherence scheme that makes use of electromagnetically induced transparency effects to achieve group-velocity slowdown. We apply a many-particle approach based on realistic semiconductor parameters that allows us to calculate the quantum dot material dynamics including microscopic carrier scattering and polarization dephasing dynamics. The group-velocity reduction is characterized in the frequency domain by a quasiequilibrium slowdown factor and in the time domain by the probe-pulse slowdown obtained from a calculation of the spatiotemporal material dynamics coupled to the propagating optical field. The group-velocity slowdown in the quantum dot molecule is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots. The dependencies of slowdown and shape of the propagating probe pulses on lattice temperature and drive intensities are investigated.
We investigate theoretically the slowdown of optical pulses due to quantum-coherence effects in InGaAs-based quantum dots and quantum dot molecules. Simple models for the electronic structure of quantum dots and, in particular, quantum-dot molecules are described and calibrated using numerical simulations. It is shown how these models can be used to design optimized quantum-dot molecules for quantum coherence applications. The wave functions and energies obtained from the optimizations are used as input for a microscopic calculation of the quantum-dot material dynamics including carrier scattering and polarization dephasing. The achievable group velocity slowdown in quantum-coherence V schemes consisting of quantum-dot molecule states is shown to be substantially higher than what is achievable from similar transitions in typical InGaAs-based single quantum dots.