Échange de spin et dynamique d’aimantation d’un gaz quantique dipolaire

Abstract : This Thesis reports on several experimental studies of magnetic properties of a Chromium Bose-Einstein condensate loaded into a 3D optical lattice, focusing on the effects induced by dipolar interactions. We show that in a 3D lattice dipolar relaxation is a resonant process due to the reduction of the density of accessible orbital states. These resonances are observed for magnetic fields Bres such that the Zeeman energy released matches an excitation towards higher-energy bands of the lattice. We can thus inhibit those processes by applying a field different from Bres. Analyses of the resonances allowed us to probe the lattice 3D band structure as well as to demonstrate the effects of local interactions between atoms. We study spin exchange dynamics in a 3D lattice. We especially observed for the first time spin exchange between atoms localized in different lattice sites mediated by dipolar interactions. These studies are the first step toward a new exploration of magnetism in lattice. Varying the depth of the lattice we study these effects in the superfluid regime, well described by mean filed theories, as well as in the strongly correlated regime, whose theoretical description is still challenging. Finally, we study the evolution dynamics of two giant spins interacting through dipolar interactions. The condensate being initially splitted in half, atoms from the two clouds are prepared in opposite spin states thus producing two giant spins of plus or minus 3xN. We show that any spin dynamics is energetically inhibited for large spins which is well accounted for by a classical theory.
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Aurélie de Paz. Échange de spin et dynamique d’aimantation d’un gaz quantique dipolaire. Gaz Quantiques [cond-mat.quant-gas]. Université Paris XIII, Sorbonne Paris Cité, 2015. Français. ⟨tel-01225113v1⟩

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