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  1. Abstract

    Electronic and excitonic states in anInSbstrongly flattened ellipsoidal quantum dot (QD) with complicated dispersion law are theoretically investigated within the framework of the geometric adiabatic approximation in the strong, intermediate, and weak quantum confinement regimes. For the lower levels of the spectrum, the square root dependence of energy on QD sizes is revealed in the case of Kane’s dispersion law. The obtained results are compared to the case of a parabolic (standard) dispersion law of charge carriers. The possibility of the accidental exciton instability is revealed for the intermediate quantum confinement regime. For the weak quantum confinement regime, the motion of the exciton's center-of-gravity is quantized, which leads to the appearance of additional Coulomb-like sub-levels. It is revealed that in the case of the Kane dispersion law, the Coulomb levels shift into the depth of the forbidden band gap, moving away from the quantum confined level, whereas in the case of the parabolic dispersion law, the opposite picture is observed. The corresponding selection rules of quantum transitions for the interband absorption of light are obtained. New selection rules of quantum transitions between levels conditioned by 2D exciton center of mass vertical motion quantization in a QD are revealed. Themore »absorption threshold behavior characteristics depending on the QDs geometrical sizes are also revealed.

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  2. We study electron tunneling in binary quantum systems as double quantum dot (DQD) and double quantum well (DQW), considered as two-level systems. The Schrodinger equation for this system is reduced using single band kp-effective Hamiltonian, and is solved numerically. We calculate full electron spectrum E, n = 1,2 ... in the bi-confinement potential. The tunneling in DQD is studied in relation to two factors, a coupling coefficient W and an asymmetry factor A of the potential. The ratio W/A defines the electron localization in DQD. The cases of ideal and almost ideal DQD are examined and compared. We are modeling the effects of environmental influence and fluctuations of electrical pulse on the coherence of DQD based charge qubit. In particular, we show that the coupling in the ideal DQD (A=0) is unstable for any small fluctuations of A.