Kajan, Michael Rolf Otto: Microscopic Theory of Photon Bose-Einstein Condensation. - Bonn, 2024. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-76809
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-76809,
author = {{Michael Rolf Otto Kajan}},
title = {Microscopic Theory of Photon Bose-Einstein Condensation},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2024,
month = jul,

note = {We introduce a novel approach for analysing light-matter interactions within driven-dissipative environments. Our study centers on the interaction between dye molecule solutions and photonic cavity modes, mediated by Jaynes-Cummings coupling. These dye molecules exhibit discrete electronic and rovibrational energy levels, influenced by the surrounding thermal environment imposed by the solvent.
The principal contribution of this work lies in the development of a mapping that links the discrete-level structure of dye molecules to auxiliary bosons, subject to an additional operator constraint. This mapping facilitates the application of field theory methods, particularly leveraging the Schwinger-Keldysh formalism to address general non-equilibrium scenarios. Especially, this frame-work allows for the exact implementation of the operator constraint. It enables us to consider Markovian and non-Markovian baths coupled to the molecules. Including non-Markovian baths is of significant importance in achieving thermalisation beyond the occupation of levels and allowing to imprint the thermal fluctuation-dissipation relation onto the spectra.
The main goal of this work is to investigate the emergence of phase coherence in the photon field. Our method enables a unified treatment of photon field fluctuations and coherence dynamics, allowing the spontaneous breaking of the U (1) symmetry inherent in the Jaynes-Cummings interaction. The large dye reservoir is incorporated via a simplified Dynamical-Mean-Field Theory leveraging an expansion in the dye molecule density. We investigate the implications of broken U (1) symmetry in an open-driven context and validate the corresponding Ward identity in the phase of the Bose-Einstein condensate. This sheds light on the intricate interplay between coherence, fluctuations, and symmetry in light-matter coupled systems within driven-dissipative environments.},

url = {https://hdl.handle.net/20.500.11811/11636}

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