1,720,991 research outputs found
Electron-Hole Localization in Coupled Quantum Dots
No full textWe theoretically investigate correlated electron-hole states in vertically coupled quantum dots. Employing a prototypical double-dot confinement and a configuration-interaction description for the electron-hole states, it is shown that the few-particle ground state undergoes transitions between different quantum states as a function of the interdot distance, resulting in unexpected spatial correlations among carriers and in electron-hole localization. Such transitions provide direct manifestations of inter- and intradot correlations, which can be directly monitored in experiments
Dark-state luminescence of macroatoms at the near field
Full text linkWe theoretically analyze the optical near-field response of a semiconductor macroatom induced by local monolayer fluctuations in the thickness of a semiconductor quantum well, where the large active volume results in a strong enhancement of the light-matter coupling. We find that in the near-field regime bright and dark excitonic states become mixed, opening new channels for the coupling to the electromagnetic field. As a consequence, ultranarrow luminescence lines appear in the simulated two-photon experiments, corresponding to very long lived excitonic states, which undergo Stark shift and Rabi splitting at relatively small field intensities
Exact biexciton binding energy in carbon nanotubes using a quantum Monte Carlo approach
No full textWe performed quantum Monte Carlo (QMC) calculations for a model system of excitons and biexcitons in carbon nanotubes (CNTs) and compared the results with those of a variational approach [T.G. Pedersen, K. Pedersen, H.D. Cornean, P. Duclos, Nano Lett. 5 (2005) 291]. Due to their geometric properties, the shape of a hollow cylinder, CNTs can be treated as 2D objects. With decreasing diameter one expects them even to exhibit quasi-1D properties. In the present study the biexciton in its ground state is found to be more strongly bound than estimated before. Biexcitonic complexes are predicted to remain stable for all diameters even at room temperature. The binding energy grows significantly with decreasing diameter, showing indeed a transition from a quasi-2D system to a quasi-ID system. (c) 2007 Elsevier B.V. All rights reserved
High-finesse optical quantum gates for electron spins in artificial molecules
No full textWe propose the storage of the quantum information (qubit) in the spin of an excess electron in two vertically coupled quantum dots and its all-optical manipulation through ps-laser pulses. The auxiliary levels of the artificial molecule allow the implementation of the logical gates solely by means of stimulated Raman adiabatic passages, and the consequent suppression of the environment losses. The mapping of the spin states onto the orbital degrees of freedom results in the switch on of the dipole-dipole interaction between neighbouring qubits and thus allows the conditional dynamics (two-qubit gates) to be performed
Optical near-field mapping of excitons and biexcitons in naturally occurring semiconductor quantum dots
No full textWe calculate the near-field optical spectra of excitons and biexcitons in semiconductor quantum dots naturally occurring at interface fluctuations in GaAs-based quantum wells, using a nonlocal description of the response function to a spatially modulated electromagnetic field. The relative intensity of the lowest, far-field forbidden excitonic states is predicted; the spatial extension of the ground biexciton state is found, in agreement with recently published experiments
Spin in quantum field theory
No full textI introduce spin in field theory by emphasizing the close connection between quantum field theory and quantum mechanics. First, I show that the spinstatistics connection can be derived in quantum mechanics without relativity or field theory. Then, I discuss path integrals for spin without using spinors. Finally, I show how spin can be quantized in a path-integral approach, without introducing anticommuting variables
Signatures of molecular correlations in few-electron dynamics of coupled quantum dots
Full text linkWe study the effect of Coulomb interaction on the few-electron dynamics in coupled semiconductor quantum dots by exact diagonalization of the few-body Hamiltonian. The oscillation of carriers is strongly affected by the number of confined electrons and by the strength of the interdot correlations. Single-frequency oscillations are found for either uncorrelated or highly correlated states, while multifrequency oscillations take place in the intermediate regime. Moreover, Coulomb interaction renders few-particle oscillations sensitive to perturbations in spatial directions other than that of the tunneling, contrary to the single-particle case. The inclusion of acoustic phonon scattering does not modify the carrier dynamics substantially at short times, but it can damp oscillation modes selectively at long times
Optical excitations of a self-assembled artificial ion
No full textBy use of magnetophotoluminescence spectroscopy, we demonstrate bias-controlled single-electron charging of a single quantum dot. Neutral, single, and double charged excitons are identified in the optical spectra. At high magnetic fields one Zeeman component of the single charged exciton is found to be quenched, which is attributed to the competing effects of tunneling and spin-flip processes. Our experimental data are in good agreement with theoretical model calculations for situations where the spatial extent of the hole wave functions is smaller as compared to the electron wave function
EFFECT OF FEW PARTICLE INTERACTION ON THE ATOMIC-LIKELEVELS OF A SINGLE PARABOLIC QUANTUM DOT
No full textFew-particle Electron Dynamics in Coupled Quantum Dots with Phonon Interaction
No full textThe time evolution of a correlated multi-electron state ina semiconductor coupled quantum dot, interacting withthe acoustic phonon bath, is calculated within the masterequation formalism, including electron-electron interactionexactly through the configuration-interactionapproach. The system is evolved after an initializationphase, with the system under strong bias, leading to thecharge density mainly localized in one of the dots. Whenthe system is evolved (in unbiased condition), dampedmulti-frequency charge oscillations are found, whichstrongly depend on the 3D system geometry and initialization.We describe the approach used to obtain themulti-electron states and to include the phonon-inducedtransitions between them in the time evolution. Furthermore,the effect of a magnetic field applied in the axialdirection of the vertical double-dot cylindrical structureis discussed
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