Publikationen
Zur Non-Adiabatic Quantum Molecular Dynamics (NA-QMD):
Weitere Publikationen, Vorträge etc. (FIS)
Semiclassical hybrid dynamics for open quantum systems
Art der Abschlussarbeit
Dissertation
Autoren
- Goletz, Christoph-Marian
Betreuer
- PD Dr. rer. nat. habil. Frank Großmann
Abstract
Realistic physical systems can never be fully isolated from their environment, they ratherrninteract with each other. Therefore it is of high interest to study open quantum systems,rnparticularly effects coming from the influence of the surrounding.rnIn the present thesis, we consider environments with a finite number of degrees of freedom.rnHowever, a full quantum treatment of such an overall system can still be computationallyrnvery costly if not impossible. Therefore, we use a recently derived semiclassical hybridrnmethod [Grossmann, J. Chem. Phys. 125, 014111 (2006)], which is extended to thernpropagation of reduced densities in the context of system-bath problems. The essentialrnidea behind this method is the treatment of different degrees of freedom on different levelsrnof semiclassical approximations with different computational efforts.rnIn the first part of this thesis, for the first time, the hybrid method is applied to systemsrncoupled to thermal baths, consisting of harmonic oscillators. First, non-resonant baths arernconsidered allowing for the investigation of pure decoherence in the absence of dissipation.rnWith the anharmonic Morse oscillator serving as a test system, we show that the developedrnhybrid method is a very efficient method, capable of reproducing decoherence effects,rnlike the quenching of interference fringes, quantum-to-classical transition and the mixing ofrnquantum states. In the same test system, quantum revivals and their bath-induced suppressionrnare investigated along with the underlying semiclassical mechanism. A fundamentalrnexperiment from the early days of quantum physics is then studied in the framework ofrnnon-resonant baths, i.e. the double slit scenario. Here, the coupling to the bath is locallyrnrestricted and we show, that the hybrid method is an appropriate tool for the treatment ofrnsimilar problems containing a coupling form factor.rnFurthermore, we study resonant baths allowing for dissipation. With both, the harmonicrnand anharmonic oscillators at hand, we investigate the accuracy of the hybrid method asrnwell as the importance of particular bath modes by comparing the respective results withrnresults obtained with an implicit method, which describes an infinite bath.rnIn the last part of this thesis, we shift away from systems in Caldeira-Leggett bathsrntowards systems in environments, whose specific form or geometry is fully describable andrnthat are nonlinearly coupled to the system. For this purpose, we refer to an experiment,rnwhere the vibrational dynamics of an Iodine diatomic molecule in a Krypton environmentrnare studied. In a model with reduced dimensionality, we first compare full quantum resultsrnwith hybrid ones showing an excellent agreement even for the degrees of freedom treatedrnwith the cruder semiclassical approximation. In the next step we increase the number ofrndegrees of freedom beyond the applicability of full quantum methods, like the split-operatorrnscheme, and find the hybrid approach to be appropriate for the investigation of the presentrnproblem opening the door for studying further and larger systems of a similar kind.
Zugeordnete Forschungsschwerpunkte
- Dissipation und Rauschen in der Quantentheore
- Semiklassische Quantentheorie
Zugeordnete Forschungsprojekte
- Dekohärenz und Dissipation in der Quantentheorie
- Semiklassische Anfangswertverfahren
Schlagwörter
semiclassical Herman Kluk propagator, dissipation and decoherence
Berichtsjahr
2011