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Effective descriptions accounting for the evolution of quantum systems that are acted on by a bath are desirable. As the number of bath degrees of freedom increases and full quantum simulations turn out computationally prohibitive, simpler models become essential to understand and gain an insight into the main physical mechanisms involved in the system dynamics. In this regard, vibrational decoherence of an [I.sub.2] diatomics is tackled here within the framework of Markovian quantum state diffusion. The [I.sub.2] dynamics are analyzed in terms of an effective decoherence rate, Λ, and the specific choice of the initial state, in particular, Gaussian wave packets and two-state superpositions. It is found that, for Markovian baths, the relevant quantity regarding decoherence is the product of friction (η) and temperature (T); there is no distinction between varying one or the other. It is also observed that decoherence becomes faster as the energy levels involved in the system state correspond to higher eigenvalues. This effect is due to a population redistribution during the dynamical process and an eventual irreversible loss of the initial coherence. These results have been compared with those available in the literature from more detailed semiclassical IVR simulations, finding a good agreement. Key words: Markovian dynamics, quantum state diffusion, vibrational decoherence, dephasing, stochastic quantum trajectory. Il est necessaire de fournir des descriptions claires expliquant l'evolution des systemes quantiques soumis aun bain. Etant donne que le nombre de degres de liberte du bain augmente et que les simulations quantiques totales sont hors de portes des calculs, il devient essentiel de recourir a des modeles simplifies pour pouvoir comprendre et apprehender les principaux mecanismes physiques impliques dans la dynamique des systemes. A cet egard, la decoherence vibrationnelle d'une molecule diatomique [I.sub.2] est integree au cadre de la diffusion quantique markovienne. La dynamique de la molecule diatomique [I.sub.2] est analysee du point de vue d'un taux decoherence effective, Λ, et du choix specifique de l'etat initial, en particulier, des paquets d'ondes gaussiens et des superpositions a deux etats. On constate, dans les bains markoviens, que la quantite adequate liee a la decoherence est le produit du frottement (η) et de la temperature (T); faire varier l'une ou l'autre de ces grandeurs revient au meme. On observe egalement que la decoherence s'accelere lorsque les niveaux d'energie mis en ceuvres dans l'etat du systeme correspondent a des valeurs propres plus elevees. Cet effet est du a une redistribution de population durant le processus dynamique et, finalement, a une perte irreversible de la coherence initiale. Ces resultats ont ete compares a ceux decrits dans la litterature et obtenus a partir de simulations IVR semiclassiques plus approfondies et ont fait apparaitre une bonne corroboration. [Traduit par la Redaction] Mots-cles: dynamique markovienne, diffusion quantique, decoherence vibrationnelles, dephasage, trajectoire quantique stochastique., I. Introduction Consider a quantum system (S) coupled to a quantum bath (B). As it is commonly done in open quantum system theory, (1) let us also assume that initially [...]

Abstract: Bohmian mechanics allows to visualize and understand the quantum-mechanical behavior of massive particles in terms of trajectories. As shown by Bialynicki-Birula, Electromagnetism also admits a hydrodynamical formulation when the existence of a wave function for photons (properly defined) is assumed. This formulation thus provides an alternative interpretation of optical phenomena in terms of photon trajectories, whose flow yields a pictorial view of the evolution of the electromagnetic energy density in configuration space. This trajectory-based theoretical framework is considered here to study and analyze the outcome from Young-type diffraction experiments within the context of the Arago–Fresnel laws. More specifically, photon trajectories in the region behind the two slits are obtained in the case where the slits are illuminated by a polarized monochromatic plane wave. Expressions to determine electromagnetic energy flow lines and photon trajectories within this scenario are provided, as well as a procedure to compute them in the particular case of gratings totally transparent inside the slits and completely absorbing outside them. As is shown, the electromagnetic energy flow lines obtained allow to monitor at each point of space the behavior of the electromagnetic energy flow and, therefore, to evaluate the effects caused on it by the presence (right behind each slit) of polarizers with the same or different polarization axes. This leads to a trajectory-based picture of the Arago–Fresnel laws for the interference of polarized light. [Copyright &y& Elsevier]

Abstract: In this review we cover recent advances in the theory of the selective adsorption phenomenon that appears in light atom/molecule scattering off solid surfaces. Due to the universal van der Waals attractive interaction incoming gas particles can get trapped by the surface, this giving rise to the formation of quasi-bound states or resonances. The knowledge of the position and width of these resonances provides relevant direct information about the nature of the gas–surface interaction as well as about the evaporation and desorption mechanisms. This information can be obtained by means of a plethora of theoretical methods developed in both the energy and time domains, which we analyze and discuss here in detail. In particular, special emphasis is given to close-coupling, wave-packet, and trajectory-based formalisms. Furthermore, a novel description of selective adsorption resonances from a stochastic quantum perspective within the density matrix and Langevin formalisms, when correlations and fluctuations of the surface (considered as a thermal bath) are taken into account, is also proposed and discussed. [Copyright &y& Elsevier]