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DTSTART;TZID=Europe/Paris:20230711T103000
DTEND;TZID=Europe/Paris:20230711T130000
DTSTAMP:20260423T043734
CREATED:20230704T163107Z
LAST-MODIFIED:20230706T072940Z
UID:9146-1689071400-1689080400@fermi.univ-tlse3.fr
SUMMARY:Interaction between an electron and a skyrmion in a Néel antiferromagnet\, and combined study of families of classical spin liquids. - (Naïmo Davier / LPT / Thèses). - 11/07/23\, 10H30
DESCRIPTION:Thesis defense \nNaïmo Davier\, LPT\, Salle de Conférence FERMI 3R4 \nSummary\nIn this thesis\, we are interested in two distinct subjects\, which nevertheless have in common the fact that they deal with magnetism and topology\, and that they are both treated almost exclusively in an analytical manner. \nThe first subject concerns the behaviour of an electron in a two-dimensional Néel antiferromagnet. We are particularly interested in the presence of a very special defect called a skyrmion\, which intrinsically carries a topological charge. The case of a ferromagnetic material has already been studied and revealed that the electron is scattered by the skyrmion\, and that this scattering depends on the spin orientation of the electron and the topological charge of the skyrmion. The antiferromagnetic case turns out to be richer here\, since there is certainly a potential scattering of the electron by the skyrmion\, again involving the spin orientation of the electron and the topological charge of the skyrmion. the electron spin\, but also the possibility of the existence of electron-skyrmion bound states. In particular\, we show that the spatial structure\, energy and existence of such bound states depend on the profile of the skyrmion at hand. We begin by constructing a quantum description of the electron-skyrmion coupling\, before applying it to different relevant skyrmion profiles\, in order to illustrate the different physical consequences of this cooupling. It appears that the number of existing bound states increases with the spatial extent of the skyrmion\, and that the spatial and energy structure of these states depend very strongly on the skyrmion profile. Contrary to what intuition might suggest\, the existence of these bound states results in a global energy cost for the skyrmion and not a gain. This energy cost also turns out to be sensitive to the spatial structure of the skyrmion\, and will therefore favour certain skyrmion profiles. It also appears that pairing a skyrmion with electrons modifies the optical absorption properties locally around the skyrmion\, making it possible to detect an antiferromagnetic skyrmion. \nThe second subject concerns classical spin liquids\, a state of matter with very specific properties that has attracted great attention in recent years. We are particularly interested in a family of Hamiltonians\, having the peculiarity of beings defined on groups of spins\, and likely to harbor such states. We focus on different methods of analytical and numerical analysis to identify and characterize the different classical spin liquids obtained with this family. These methods are applied to three different Hamiltonians\, allowing us to illustrate the effectiveness of these analysis tools on the one hand\, and the richness of the spin liquids generated by this family of Hamiltonians on the other hand. Some specific characteristics of observed spin liquids are studied in detail\, thus serving as novel case studies.
URL:https://fermi.univ-tlse3.fr/event/interaction-between-an-electron-and-a-skyrmion-in-a-neel-antiferromagnet-and-combined-study-of-families-of-classical-spin-liquids-naimo-davier-lpt-theses-11-07-23-10h30/
LOCATION:Salle de conférence\, Bâtiment 3R4
CATEGORIES:Events,HDR / Thesis,LPT
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DTSTART;TZID=Europe/Paris:20230711T160000
DTEND;TZID=Europe/Paris:20230711T190000
DTSTAMP:20260423T043734
CREATED:20230703T132408Z
LAST-MODIFIED:20230706T073004Z
UID:9143-1689091200-1689102000@fermi.univ-tlse3.fr
SUMMARY:Asymmetric cloning in quantum information theory. - (Denis Rochette / LPT / Thèses). - 11/07/23\, 16H
DESCRIPTION:Soutenance de thèse \nDenis Rochette\, LPT\, Salle de Conférence FERMI 3R4 \nSummary\nThis thesis studies quantum cloning and related quantum entanglement problems using fundamental concepts of representation theory\, in particular those associated with the symmetric group. The research explores Schur-Weyl duality and its extensions\, which allow efficient representation and manipulation of quantum systems\, providing a valuable tool for quantum information theory. A main application of Schur-Weyl duality is the quantum cloning problem\, which is studied both for cases 1 → 2 and for the more general cases 1 → N\, providing new insights into the constraints imposed by the no-cloning theorem. The study is then extended to a more general quantum entanglement problem on a complete graph. The thesis is organised into chapters on Schur-Weyl duality\, the mathematical foundations of quantum mechanics\, quantum cloning problems and quantum entanglement problems\, with an appendix providing an overview of representation theory.
URL:https://fermi.univ-tlse3.fr/event/asymmetric-cloning-in-quantum-information-theory-denis-rochette-lpt-theses-11-07-23-14h/
LOCATION:Salle de conférence\, Bâtiment 3R4
CATEGORIES:Events,HDR / Thesis,LPT
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