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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Institut für Theoretische Physik IInstitute: search.filters.UBSInstitut.Fakultätsübergreifend / Sonstige EinrichtungStart date: 2020Publication Type: search.filters.UBSTyp.Dissertation

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    Quantum cooling : thermodynamics and information
    (2023) Soldati, Rodolfo R.; Lutz, Eric (Prof. Dr.)
    The theory of cooling is an important corner of thermodynamics, underlying many modern technological applications. As the field of quantum thermodynamics advances, refrigeration techniques must keep pace to fuel the innovations of quantum technologies. We study quantum cooling from its foundations to laboratory implementations within the specific paradigm of heat bath algorithmic cooling. Our study includes a detail modeling of experimental imperfections and establishes the fundamental cooling limits of the model, consolidating the algorithm as a viable quantum refrigeration method. Next, by developing the notion of virtual qubits, we demonstrate a cooling-boost protocol fueled by quantum coherences which is robust to experimental implementations. Aiming at aiding in the progress of refrigeration technologies, we conclude by studying the zero temperature equilibrium properties of a many-body system that can accommodate an autonomous quantum absorption refrigerator, and calculate its entanglement and critical properties, two features that, like quantum coherences, promise to improve the performance of quantum coolers.
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    ItemOpen Access
    Fluctuation theorems for non-Gaussian processes and disordered baths : quantum and classical
    (2025) Faria, Arthur M.; Lutz, Eric (Prof. Dr.)
    Non-Gaussian noise is omnipresent in systems where the central-limit theorem is inapplicable. We investigate the stochastic thermodynamics of small systems described by a general Kramers-Moyal equation with both Gaussian and non-Gaussian white noise, obtaining detailed and integral fluctuation relations for non-equilibrium entropy production in the small-noise regime. These results extend to phase space, where we examine whether the integral fluctuation theorem holds for Markovian non-Gaussian noises and characterize their non-equilibrium thermodynamics. These theoretical results manifest in inhomogeneous environments with finite-range system-bath coupling, where finite correlation lengths induce non-Gaussian Markovian noise via higher-order terms in the Kramers-Moyal equation; analytical solutions for the overdamped harmonic oscillator in this regime explicitly demonstrate non-Gaussian diffusion and non-trivial steady-state statistics. Building on these findings, we numerically study a driven system with localized bath interactions, including overdamped or underdamped particles in dragged harmonic potentials, where systematically reducing the interaction range leads to two main effects: dramatic enhancement of non-Gaussian signatures accompanied by strong suppression of mean entropy production. Finally, in the overdamped regime, we further discuss a generalized detailed-balance condition that defines a dynamic structure factor for the environment’s non-Gaussian density fluctuations, making it directly measurable in scattering experiments