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Quantum Dot System (quantum + dot_system)
Selected AbstractsExcitation dynamics in a three-quantum dot system driven by optical near-field interaction: towards a nanometric photonic deviceJOURNAL OF MICROSCOPY, Issue 3 2003K. Kobayashi Summary Using density operator formalism, we discuss interdot excitation energy transfer dynamics driven by the optical near-field and phonon bath reservoir, as well as coherent excitation dynamics of a quantum dot system. As an effective interaction between quantum dots induced by the optical near-field, the projection operator method gives a renormalized dipole interaction, which is expressed as a sum of the Yukawa functions and is used as the optical near-field coupling of quantum dots. We examine one- and two-exciton dynamics of a three-quantum dot system suggesting a nanometric photonic switch, and numerically obtain a transfer time comparable with the recent experimental results for CuCl quantum dots. [source] Temperature dependences of charged excitons in low-density InAs quantum dot systemPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008M. Ohmori Abstract Photoluminescence (PL) studies have been made on a single self-organized InAs quantum dot system at temperatures T from 11 to 140 K in a unique sample where the average inter-dot distance exceeds 10 ,m. While PL from neutral excitons is the strongest in the low and high temperature ranges, PL are dominated by those from negatively charged excitons when T is between 40 and 80 K. It is suugested this phenomenon is probably caused by the difference in diffusivities of photogenerated electrons and holes that gets maximum in the intermediate range. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Single-particle state mixing and Coulomb localization in two-electron realistic coupled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007Dmitriy V. Melnikov Abstract The exchange coupling in a realistic double quantum dot system is computed as a function of the gate confinement and magnetic field using a hybrid multiscale approach where the many-body Schrödinger equation is solved exactly within the full quantum dot device environment. It is found that at zero magnetic field the exchange energy varies from meV to sub-,eV value as the confinement gate biases (tunneling barrier) are changed and the system is driven from a single quantum dot to two coupled quantum dots. At the same time the magnetic field of the singlet-triplet transition is weakly affected by the changes and remains at about 1 T in the same range of the gate biases. The small values of the exchange coupling in this structure are attributed to the large inter-electron separation arising when the Coulomb repulsion dominates tunneling. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Correlation studies in weakly confining quantum dot potentialsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Peter Kimani Abstract We investigate the electron correlation in few-electron closed-shell atomic systems and similarly in few-electron quantum dots under weak confinement. As usual we start with restricted Hartree,Fock (HF) calculations and add electron correlation in steps in a series of approximations based on the single particle Green's function approach: (i) second-order Green function (GF); (ii) 2ph -Tamm-Dancoff approximation (TDA); and (iii) an extended version thereof which introduces ground-state correlation into the TDA. Our studies exhibit similarities and differences between weakly confined quantum dots and standard atomic systems. The calculations support the application of HF, GF, and TDA techniques in the modeling of three-dimensional quantum dot systems. The observed differences emphasize the significance of confinement and electronic features unique to quantum dots, such as the increased binding of electrons with higher angular momentum and thus,compared to atomic systems,modified shell-filling sequences. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Understanding quantum dots: overheating of the LO-phonon modesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2007K. Král Abstract Longitudinal optical phonons have been used recently to explain the electronic energy relaxation in quantum dots. In this theory they served as a reservoir, on which the electron executes multiple scattering acts. Rather naturally such a phonon subsystem is expected to be passive, namely, in a long-time limit of development the whole system should be able to achieve such a stationary state in which statistical distributions of both subsystems, electron and phonons, do not change in time. Here we remind briefly that the recent approach to the relaxation theory in quantum dots displays a non-passivity of such a reservoir. We remind briefly the method of a partial elimination of this phonon overheating effect by using the Lang-Firsov transformation. We apply the modified relaxation theory to the electronic relaxation at low electronic densities in quantum dot systems and come to conclusions about the role of e-LO scattering mechanism in these situations. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Solid-immersion-lens-enhanced nanophotoluminescence for spectroscopy of quantum dot systemsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003Bénédicte Dal Don Abstract We present a novel experimental setup, which introduces a solid-immersion-lens (SIL) into a confocal microphotoluminescence system. This non-destructive method allows us, within a field of view of 35,,m, to reach a spatial resolution of about 200 nm, which is comparable to near-field systems. We demonstrate an enhancement of the collection efficiency by a factor of five in comparison to standard confocal setups. This is very important for single-dot spectroscopy, where the excitation and detection signals are very low. Moreover, we prove that the spatial resolution and collection efficiency of the system are quite insensitive to air gaps which could be formed at the interface between sample and SIL. These two features can be explained with theoretical considerations. For all these reasons, the system is very suitable for the study of single excitonic lines in quantum dots. We show its application in polarization- and temperature-dependent studies. [source] Phonon-assisted tunnelling in coupled quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003H. B. Sun Abstract We apply a quantum master equation approach to coupled quantum dot systems that involve inelastic transitions between the dots. The Hamiltonian we use to model the inelastic interaction between electrons and the phonon bath differs from those of other papers. The calculated current spectra as a function of temperature and the coherent tunnelling rate are consistent with experimental results. The model is applicable to similar systems involving interactions between electrons and different types of bosons. [source] Generation of three-qubit entangled states using coupled multi-quantum dotsLASER PHYSICS LETTERS, Issue 5 2007M. Abdel-Aty Abstract We discuss a mechanism for generating a maximum entangled state (Greenberger,Horne,Zeilinger (GHZ)) in a coupled quantum dots system, based on analytical techniques. The reliable generation of such states is crucial for implementing solid-state based quantum information schemes. The signature originates from a remarkably weak field pulse or a far offresonance effects which could be implemented using technology that is currently being developed. The results are illustrated with an application to a specific wide-gap semiconductor quantum dots system, like Zinc Selenide (ZnSe) based quantum dots. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] | ||||||||||