250 research outputs found

    Exact two-body quantum dynamics of an electron-hole pair in semiconductor coupled quantum wells: a time-dependent approach

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    We simulate the time-dependent coherent dynamics of a spatially indirect exciton (an electron-hole pair with the two particles confined in different layers) in a GaAs coupled quantum well system. We use a unitary wave-packet propagation method taking into account in full the four degrees of freedom of the two particles in a two-dimensional system, including both the long-range Coulomb attraction and arbitrary two-dimensional electrostatic potentials affecting the electron and/or the hole separately. The method has been implemented for massively parallel architectures to cope with the huge numerical problem, showing good scaling properties and allowing evolution for tens of picoseconds. We have investigated both transient time phenomena and asymptotic time transmission and reflection coefficients for potential profiles consisting of i) extended barriers and wells and ii) a single-slit geometry. We found clear signatures of the internal two-body dynamics, with transient phenomena in the picosecond time-scale which might be revealed by optical spectroscopy. Exact results have been compared with mean-field approaches which, neglecting dynamical correlations by construction, turn out to be inadequate to describe the electron-hole pair evolution in realistic experimental conditions.Comment: 12 two-column pages + 3 supplemental material pages, 9 figures, to appear on Phys.Rev.

    A virtual roundtable on Iser’s legacy Part IV: a conversation with Federico Bertoni

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    In this article you find the fourth and last part of our ‘virtual roundtable’ on Wolfgang Iser’s legacy with Gerald Prince, Mark Fremman, Marco Caracciolo and Federico Bertoni. In part IV we discuss with Federico Bertoni the state of theories of reading and the centality of Iser’s work in the field, the ethical potential of literature, and the role of literary criticism and theory today

    Time-dependent scattering of a composite particle: A local self-energy approach for internal excitations

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    When composite particles - such as small molecules, nuclei, or photogenerated excitons in semiconductors - are scattered by an external potential, energy may be transferred between the c.m. and the internal degrees of freedom. An accurate dynamical modeling of this effect is pivotal in predicting diverse scattering quantities and reaction cross sections, and allows us to rationalize time-resolved energy and localization spectra. Here, we show that time-dependent scattering of a quantum composite particle with an arbitrary, nonperturbative external potential can be obtained by propagating the c.m. degrees of freedom with a properly designed local self-energy potential. The latter embeds the effect of internal virtual transitions and can be obtained by the knowledge of the stationary internal states. The case is made by simulating Wannier-Mott excitons in one- and two-dimensional semiconductor heterostructures. The self-energy approach shows very good agreement with numerically exact Schr\uf6dinger propagation for scattering potentials where a mean-field model cannot be applied, at a dramatically reduced computational cost

    Prefazione

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    Il testo è un'introduzione critica al volume di Carati, incentrato sulla narrativa americana contemporanea e a una rosa di questioni teoriche che riguardando la configurazione narrativa dell'esperienza

    Programmazione dinamica per opzioni Americane

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    Questa tesi affronta in modo approfondito le opzioni Americane e il problema dell'individuazione di un prezzo per queste ultime. Dopo uno studio del problema a tempo discreto viene affrontato anche quello a tempo continuo. In particolare, si analizza il problema a frontiera libera dando risultati teorici sull'esistenza di una soluzione forte. Infine, tramite un'implementazione dinamica in Matlab, vengono visualizzati alcuni grafici per lo studio del comportamento del prezzo di una put Americana al variare di alcuni parametri. Infine si mostra la frontiera del problema ad ostacolo in due diversi spazi per una put Americana
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