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arXiv:1404.2780 · Physical Review B

Group-velocity slowdown in a double quantum dot molecule

Stephan Michael, Weng W. Chow, Hans Christian Schneider

Published Sep 13, 2013• 27 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/physrevb.88.125305

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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.
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.
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.
The authors demonstrate theoretically that there exists electromagnetically induced transparency in an asymmetric double quantum dot system using tunneling instead of pump laser. The group velocity slowdown factor is theoretically analyzed as a function of electron tunneling at different broadened linewidths. With feasible parameters for applications to a 100Gbits∕s optical network, numerical calculation infers group velocity as low as 300m∕s. The scheme is expected to be useful in constructing a variable semiconductor optical buffer based on electromagnetically induced transparency in an asymmetric double quantum dot controlled by voltage.
Abstract This paper presents the dynamics of Kerr nonlinearity and the phenomenon of slow group velocity in a Quantum Dot (QD) system, using the mechanism of electromagnetically induced transparency (EIT). Employing a three-level QD setup and leveraging a ladder-type excitation approach, we analyse the interaction between a weak probe pulse and a strong control beam. By employing density matrix formalism, we derive the expressions for both linear and nonlinear optical susceptibilities, along with first-order linear dispersion terms. Our findings reveal that susceptibilities in the QD system, both linear and nonlinear, can be finely adjusted to desired probe frequencies through control parameter manipulation. Moreover, under the EIT regime, we observe the Kerr susceptibility on the order of 10−12 m2 V2 at a probe wavelength 1.359 μm. Additionally, the group velocity of the probe field experiences a remarkable slowdown by a factor of 103 compared to the speed of light in vacuum. Results obtained may have potential applications in fabricating nonlinear optical devices.
Tunneling-induced transparency in vertically coupled InGaAs/GaAs quantum dots using tunneling instead of pump laser, analogous to electromagnetically induced transparency in atomic systems, is studied. The interdot quantum coupling strength is tuned by static electric fields. The group velocity slow-down factor is theoretically analyzed as a function of electron tunneling at different broadened linewidths. For parameters appropriate to a 100 Gbits/s optical network, group velocities as low as 850 m/s are calculated. The scheme is expected to be useful to construct a variable semiconductor optical buffer based on electromagnetically induced transparency in vertically coupled InGaAs/GaAs quantum dots controlled by electric fields.