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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Institut für Theoretische Physik IStart date: 2020End date: 2022Publication Type: search.filters.UBSTyp.Zeitschriftenartikel

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    Analysis of the fine structure of the D‐exciton shell in cuprous oxide
    (2021) Heckötter, Julian; Rommel, Patric; Main, Jörg; Aßmann, Marc; Bayer, Manfred
    The exciton states in cuprous oxide show a pronounced fine structure splitting associated with the crystal environment and the resulting electronic band structure. High‐resolution spectroscopy reveals an especially pronounced splitting of the yellow D excitons with one state pushed above any other state with the same principal quantum number. This large splitting offset is related to a strong mixing of these D states with the 1S exciton of the green series, as suggested by previously published calculations. Here, a detailed comparison of this theory with experimental data is given, which leads to a complete reassignment of the experimentally observed D exciton lines. The origin of different amounts of green admixture to D‐envelope states is deduced by analyzing the different terms of the Hamiltonian. The yellow-green mixing leads to level repulsion and induces an exchange interaction splitting to D‐envelope states, from which one of them becomes the highest state within each multiplet. Furthermore, the assignment of D exciton states according to their total angular momentum F is given and corrects an earlier description given in a former study.
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    ItemOpen Access
    A quantum heat engine driven by atomic collisions
    (2021) Bouton, Quentin; Nettersheim, Jens; Burgardt, Sabrina; Adam, Daniel; Lutz, Eric; Widera, Artur
    Quantum heat engines are subjected to quantum fluctuations related to their discrete energy spectra. Such fluctuations question the reliable operation of thermal machines in the quantum regime. Here, we realize an endoreversible quantum Otto cycle in the large quasi-spin states of Cesium impurities immersed in an ultracold Rubidium bath. Endoreversible machines are internally reversible and irreversible losses only occur via thermal contact. We employ quantum control to regulate the direction of heat transfer that occurs via inelastic spin-exchange collisions. We further use full-counting statistics of individual atoms to monitor quantized heat exchange between engine and bath at the level of single quanta, and additionally evaluate average and variance of the power output. We optimize the performance as well as the stability of the quantum heat engine, achieving high efficiency, large power output and small power output fluctuations.