Universität zu Köln

Fröml, Heinrich Filon (2020). Localized Dissipation in Fermionic Quantum Wires. PhD thesis, Universität zu Köln.

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Abstract

Localized dissipation in many-body quantum systems represents an emergent focal point of non-equilibrium physics. In recent experiments, localized particle losses were realized in ultracold atomic gases, thus opening up new avenues for investigating the interplay between many-body and non-equilibrium effects. The main focus of this work is the theoretical study of collective phenomena in one-dimensional systems of interacting spinless fermions subject to a localized loss. This model constitutes a non-equilibrium counterpart of the paradigmatic Kane-Fisher potential barrier problem. In particular, strong interaction effects emerge due to the gapless nature of the system. We show that the loss and transport properties of the quantum wire in the presence of a localized loss are drastically modified by interactions as a result of the interplay between coherent and incoherent processes. In experiments with localized losses, a manifestation of the quantum Zeno effect is encountered, which can be described exhaustively in terms of local, microscopic physics. In contrast, we demonstrate that the interplay of gapless quantum fluctuations and particle interactions with the localized dissipation leads to an instance of the quantum Zeno effect of genuine many-body nature. After the localized losses are switched on, a non-equilibrium steady state emerges in the quantum wire. We derive exact results for the properties of this steady state in the non-interacting limit and formulate a theoretical description of the depletion processes by introducing the momentum-dependent loss probability of modes. Remarkably, we find that coherence properties of the initial state persist, leading to the formation of Friedel oscillations near the loss site. The presence of interactions between the fermions modifies the dynamics in the wire and leads to an energy-dependent renormalization of loss processes. We find that the loss probability is strongly renormalized for modes with an energy close to the Fermi energy, leading to the suppression of losses at the Fermi level. In the case of repulsive interactions, the suppression of losses is accompanied by the loss site becoming completely opaque, which establishes a fluctuation-induced quantum Zeno effect. For attractive interactions, instead, the localized loss becomes fully transparent to particles at the Fermi level, resulting accordingly in the suppression of losses as a fluctuation-induced transparency. The strong modifications of the loss properties are reflected in observables such as the momentum distribution in the wire, exhibiting an increased occupation at the Fermi momentum. In addition, we study the influence of self-thermalization effects on the renormalization of the effective dissipation strength. Here, we identify regimes where the generation of an effective temperature is sufficiently weak to achieve significant renormalization. Furthermore, the microscopic quantum Zeno effect affects the spectral properties of the non-Hermitian Hamiltonian associated with a localized loss for a lattice model. Here, a sharp reorganization of the spectrum is encountered at a critical dissipation strength, causing a characteristic signature in the response properties of the wire. We investigate the interplay of interactions in the wire and localized dissipation within three complementary approaches. In a microscopic real-space renormalization group analysis the physical mechanisms behind the modified depletion properties are particularly transparent. Within a dynamical Hartree-Fock approximation the resulting effects on observables such as the momentum distribution in the non-equilibrium steady states can be studied. Finally, an effective Luttinger liquid description demonstrates the universality of the findings and enables the investigation of mode-coupling effects.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Fröml, Heinrich Filon UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-116474
Date:	2020
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute for Theoretical Physics
Subjects:	Physics
Uncontrolled Keywords:	Keywords Language Open quantum systems English Non-equilibrium physics English Quantum many-body systems English Quantum wires English Localized dissipation English Localized loss English Collective phenomena English Quantum Zeno effect English
Date of oral exam:	26 June 2020
Referee:	Name Academic Title Diehl, Sebastian Prof. Dr. Rosch, Achim Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/11647