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      Phonon-induced decay of the electron spin in quantum dots

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          Abstract

          We study spin relaxation and decoherence in a GaAs quantum dot due to spin-orbit interaction. We derive an effective Hamiltonian which couples the electron spin to phonons or any other fluctuation of the dot potential. We show that the spin decoherence time \(T_2\) is as large as the spin relaxation time \(T_1\), under realistic conditions. For the Dresselhaus and Rashba spin-orbit couplings, we find that, in leading order, the effective magnetic field can have only fluctuations transverse to the applied magnetic field. As a result, \(T_2=2T_1\) for arbitrarily large Zeeman splittings, in contrast to the naively expected case \(T_2\ll T_1\). We show that the spin decay is drastically suppressed for certain magnetic field directions and values of the Rashba coupling constant. Finally, for the spin coupling to acoustic phonons, we show that \(T_2=2T_1\) for all spin-orbit mechanisms in leading order in the electron-phonon interaction.

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          Allowed and forbidden transitions in artificial hydrogen and helium atoms

          The strength of radiative transitions in atoms is governed by selection rules. Spectroscopic studies of allowed transitions in hydrogen and helium provided crucial evidence for the Bohr's model of an atom. Forbidden transitions, which are actually allowed by higher-order processes or other mechanisms, indicate how well the quantum numbers describe the system. We apply these tests to the quantum states in semiconductor quantum dots (QDs), which are regarded as artificial atoms. Electrons in a QD occupy quantized states in the same manner as electrons in real atoms. However, unlike real atoms, the confinement potential of the QD is anisotropic, and the electrons can easily couple with phonons of the material. Understanding the selection rules for such QDs is an important issue for the manipulation of quantum states. Here we investigate allowed and forbidden transitions for phonon emission in one- and two-electron QDs (artificial hydrogen and helium atoms) by electrical pump-and-probe experiments, and find that the total spin is an excellent quantum number in artificial atoms. This is attractive for potential applications to spin based information storage.
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            Author and article information

            Journal
            2003-10-28
            Article
            10.1103/PhysRevLett.93.016601
            cond-mat/0310655
            ec0a4134-d5e9-491d-b61c-c9dca4a69928
            History
            Custom metadata
            Phys. Rev. Lett. 93, 016601 (2004)
            5 pages, 1 figure
            cond-mat.mes-hall

            Nanophysics
            Nanophysics

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