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ABSTRACT: Single quantum dot molecules have been fabricated from coupled quantum well structures of (Cd, Mn, Mg) Te alloy materials using a selective interdiffusion technique. Incorporation of Mn ions in one of the quantum dots in the molecule results in pairs of quantum dots with markedly different spin splittings. By comparing the observed magnetic field dependence of the optical polarization in photoluminescence with detailed calculations, we show that the coupling between the dots is quantum mechanical tunnel coupling and that it is tunable.
Journal of Applied Physics 07/2008; · 2.17 Impact Factor
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ABSTRACT: We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge-tunable quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wave functions through asymmetric e-e and e-h exchange interactions.
Physical Review Letters 11/2005; 95(17):177403. · 7.37 Impact Factor
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ABSTRACT: Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.
Physical Review Letters 05/2005; 94(15):157401. · 7.37 Impact Factor
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ABSTRACT: The optically induced indirect exchange interaction between spins in two quantum dots is investigated theoretically. We present a microscopic formulation of the interaction between the localized spin and the itinerant carriers including the effects of correlation, using a set of canonical transformations. Correlation effects are found to be of comparable magnitude as the direct exchange. We give quantitative results for realistic quantum dot geometries and find the largest couplings for one dimensional systems. Comment: 4 pages, 3 figures
11/2004;
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ABSTRACT: Results are given for spin relaxation in quantum dots due to acoustic phonon-assisted flips of single spins at low temperatures. The dominant spin relaxation processes for varying dot size, temperature, and magnetic field are identified. These processes are mediated by the spin-orbit interaction and are described within a generalized effective mass treatment. Particular attention is given to phonon coupling due to interface motion, which dominates the relaxation for dots with diameters ≲15nm, and also to a direct spin-phonon process that arises from valence-conduction band coupling and dominates the rates for increasing temperature. Low-temperature relaxation rates are found to be small and to depend strongly on size, on temperature, and on magnetic field. Results are illustrated with evaluations for GaAs/AlxGa1-xAs systems, and a minimum in the relaxation rate is found for dot diameters ∼20nm.
Phys. Rev. B. 66(16).
