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Acta Physica Polonica A

Superradiance Effects in the Linear and Nonlinear Optical Response of Quantum Dot Molecules

Anna Sitek, Paweł Machnikowski

Published Nov 1, 2008• 1 citation
Publisher

Abstract

We calculate the linear optical response from a single quantum dot molecule and the nonlinear, four-wave-mixing response from an inhomogeneously broadened ensemble of such molecules.We show that both optical signals are affected by the coupling-dependent superradiance effect and by optical interference between the two polarizations.As a result, the linear and nonlinear responses are not identical.

DOI
10.12693/aphyspola.114.1355

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In the present study, the effect of the geometrical shape of quantum dots on the nonlinear absorption coefficient of semiconductor quantum dot molecules (QDMs) is theoretically investigated. The nonlinear optical response of QDMs is analyzed using the density matrix formalism, because this theoretical framework provides a rigorous and unified method to describe the interaction between electromagnetic fields and confined carriers, enabling the derivation of both linear and higher-order nonlinear susceptibilities. Accordingly, the nonlinear optical absorption of double quantum dot molecules, triple quantum dot molecules, and quadruple quantum dot molecules coupled through tunneling is studied and compared. We show that the optical spectral response of QDMs is significantly affected by their shape and the strength of tunneling between coupled quantum dots of a QDM. The results indicate that the shape of quantum dots can significantly affect nonlinear optical absorption. In addition, the tunneling intensity between the closely quantum dots strongly affects the nonlinear absorption, and the width and number of transparency windows.
In the present work, the linear and nonlinear optical properties of quantum dot molecules composed of two quantum dots as well as three quantum dots molecules, respectively known as double quantum dot (DQD) molecule and triple quantum dot (TQD) molecules are studied using the probability amplitude method, and the obtained results are discussed and compared. By solving the state equations of these systems in the interaction picture, under the rotating wave approximation and the dipole approximation, the first and third-order susceptibilities for DQD and TQD molecules are calculated. A phenomenon called tunneling-induced transparency (TIT) which is similar to electromagnetically induced transparency (EIT) is studied in these types of quantum dot molecules. The effect of key system parameters such as tunneling couplings between quantum dots and the tunneling intensity on the linear and nonlinear optical response of multiple quantum dot molecules DQD and TQD is investigated. It was shown that the position and the width of the TIT window created in these quantum dot molecules can be tuned by changing the physical parameters.
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