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2004

Electron-nuclei spin relaxation through phonon-assisted hyperfine interaction in a quantum dot

V A Abalmassov, F Marquardt

Physical Review B 70 (7) 075313 (2004) | Journal | PDF

We investigate the inelastic spin-flip rate for electrons in a quantum dot due to their contact hyperfine interaction with lattice nuclei. In contrast to other works, we obtain a spin-phonon coupling term from this interaction by taking directly into account the motion of nuclei in the vibrating lattice. In the calculation of the transition rate the interference of first and second orders of perturbation theory turns out to be essential. It leads to a suppression of relaxation at long phonon wavelengths, when the confining potential moves together with the nuclei embedded in the lattice. At higher frequencies (or for a fixed confining potential), the zero-temperature rate is proportional to the frequency of the emitted phonon. We address both the transition between Zeeman sublevels of a single electron ground state as well as the triplet-singlet transition, and we provide numerical estimates for realistic system parameters. The mechanism turns out to be less efficient than electron-nuclei spin relaxation involving piezoelectric electron-phonon coupling in a GaAs quantum dot.

Relaxation and dephasing in a many-fermion generalization of the Caldeira-Leggett model

Relaxation and dephasing in a many-fermion generalization of the Caldeira-Leggett model

F Marquardt, D S Golubev

Physical Review Letters 93 (13) 130404 (2004) | Journal | PDF

We analyze a model system of fermions in a harmonic oscillator potential under the influence of a fluctuating force generated by a bath of harmonic oscillators. This represents an extension of the well-known Caldeira-Leggett model to the case of many fermions. Using the method of bosonization, we calculate Green's functions and discuss relaxation and dephasing of a single extra particle added above the Fermi sea. We also extend our analysis to a more generic coupling between system and bath that results in complete thermalization of the system.

Effects of dephasing on shot noise in an electronic Mach-Zehnder interferometer

Effects of dephasing on shot noise in an electronic Mach-Zehnder interferometer

F Marquardt, C Bruder

Physical Review B 70 (12) 125305 (2004) | Journal | PDF

We present a theoretical study of the influence of dephasing on shot noise in an electronic Mach-Zehnder interferometer. In contrast to phenomenological approaches, we employ a microscopic model where dephasing is induced by the fluctuations of a classical potential. This enables us to treat the influence of the environment's fluctuation spectrum on the shot noise. We compare against the results obtained from a simple classical model of incoherent transport, as well as those derived from the phenomenological dephasing terminal approach, arguing that the latter runs into a problem when applied to shot-noise calculations for interferometer geometries. From our model, we find two different limiting regimes: If the fluctuations are slow as compared to the time scales set by voltage and temperature, the usual partition noise expression T(1-T ) is averaged over the fluctuating phase difference. For the case of "fast" fluctuations, it is replaced by a more complicated expression involving an average over transmission amplitudes. The full current noise also contains other contributions, and we provide a general formula, as well as explicit expressions and plots for specific examples.

Influence of dephasing on shot noise in an electronic Mach-Zehnder interferometer

Influence of dephasing on shot noise in an electronic Mach-Zehnder interferometer

F Marquardt, C Bruder

Physical Review Letters 92 (5) 056805 (2004) | Journal | PDF

We analyze shot noise under the influence of dephasing in an electronic Mach-Zehnder interferometer, of the type that was realized recently [Yang Ji et al., Nature (London) 422, 415 (2003)]. Using a model of dephasing by a fluctuating classical field, we show how the usual partition noise expression T(1-T) is modified. We study the dependence on the power spectrum of the field, which is impossible in simpler approaches such as the dephasing terminal, against which we compare. We remark on shot noise as a tool to distinguish thermal smearing from genuine dephasing.

Perturbative corrections to the Gutzwiller mean-field solution of the Mott-Hubbard model

Perturbative corrections to the Gutzwiller mean-field solution of the Mott-Hubbard model

C Schroll, F Marquardt, C Bruder

Physical Review A 70 (5) 053609 (2004) | Journal | PDF

We study the Mott-insulator transition of bosonic atoms in optical lattices. Using perturbation theory, we analyze the deviations from the mean-field Gutzwiller ansatz, which become appreciable for intermediate values of the ratio between hopping amplitude and interaction energy. We discuss corrections to number fluctuations, order parameter, and compressibility. In particular, we improve the description of the short-range correlations in the one-particle density matrix. These corrections are important for experimentally observed expansion patterns, both for bulk lattices and in a confining trap potential.

Contact

Theory Division
Prof. Florian Marquardt

Max Planck Institute for the Science of Light
Staudtstr. 2
91058 Erlangen, Germany

For all general inquiries, please contact us at:

florian.marquardt@mpl.mpg.de
anna-gesine.murphy@mpl.mpg.de

Tel: +49 9131 7133 401
Fax: +49 9131 7133 409

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