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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Institut für Theoretische Physik IStart date: 2020Author: search.filters.author.Rodrigues, Franklin L. S.

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    Nonequilibrium thermodynamics of quantum coherence beyond linear response
    (2024) Rodrigues, Franklin L. S.; Lutz, Eric
    Quantum thermodynamics allows for the interconversion of quantum coherence and mechanical work. Quantum coherence is thus a potential physical resource for quantum machines. However, formulating a general nonequilibrium thermodynamics of quantum coherence has turned out to be challenging. In particular, precise conditions under which coherence is beneficial to or, on the contrary, detrimental for work extraction from a system have remained elusive. We here develop a generic dynamic-Bayesian-network approach to the far-from-equilibrium thermodynamics of coherence. We concretely derive generalized fluctuation relations and a maximum-work theorem that fully account for quantum coherence at all times, for both closed and open dynamics. We obtain criteria for successful coherence-to-work conversion, and identify a nonequilibrium regime where maximum work extraction is increased by quantum coherence for fast processes beyond linear response.
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    Thermodynamics in the presence of initial coherences and correlations
    (2024) Rodrigues, Franklin L. S.; Lutz, Eric (Prof. Dr.)
    One of the main trends in modern technology is the constant miniaturization of electronic devices. In doing so, it is inevitable that quantum effects will eventually be an unavoidable feature in the planing and fabrication of new instruments; considerations about their power output and energy efficiency lie beyond the scope of classical physics. This regime demands a generalization of the laws of thermodynamics that accounts for the interconversion between classical and quantum resources. This thesis fills this gap by providing a general method to extend the second law of thermodynamics to account for genuine quantum features. These include state coherences consumed in the energy basis and quantum correlations between the system of interest and its environment. We show with our framework that the consumption of coherences is a necessary condition for improved work extraction. For it to be sufficient, we show that one must carefully consider the decoherence timescales. We proceed to investigate two general classes of systems in which quantum resources naturally occur. We begin by studying the thermal properties of generalized Gibbs ensembles, i.e., systems whose conserved quantities do not commute. Then, we explore open quantum systems where the steady state contains non-negligible correlations as consequence of strong interaction strengths with their enviroments. In both cases, we show under which conditions one can use quantum resources to improve the performance of thermal processes, paving the way to efficient design at the nanoscale.