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Quantum gases of Chromium : thermodynamics and magnetic properties of a Bose-Einstein condensate and production of a Fermi sea

Abstract : This thesis presents experimental results performed with Quantum gases of Chromium atoms. The specificity of Chromium resides in its large electronic spin S=3 and non negligible dipole-dipole interaction (DDI) between atoms. We produced a new quantum gas, a Fermi sea of the ⁵³Cr isotope. Optimization of the co-evaporation with the ⁵²Cr bosonic isotope leads to 10³ atoms at T=TF= 0.66± 0.08. We obtained new results on thermodynamics of a spinor Bose gas. By "shock cooling" a thermal multi-spin component gas, we find that the dynamics of the BEC is affected by spin changing collisions. We also demonstrate a new cooling mechanism based on the spin degrees of freedom when the Bose Einstein condensate (BEC) is in the lowest energy spin state. Dipolar interactions thermally populate spin excited states at low magnetic field. Purication of the BEC is obtained by selectively removing these thermal atoms. Finally, we present spin dynamics experiments. spin following preparation of atoms in a double well trap in opposite stretch spin states allow to measure the last unknown scattering length of ⁵²Cr: ɑo = 13.5 ±¹⁵ ₁₀ ɑB (with ɑB the Bohr radius). We then present preliminary results performed in a 3D lattice and in the bulk, where spin excitation is performed by a spin rotation. We investigate for different experimental congurations which of a theory with or without quantum correlations ts best our data.
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Submitted on : Thursday, November 29, 2018 - 6:15:06 PM
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  • HAL Id : tel-01939835, version 1

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Bruno Naylor. Quantum gases of Chromium : thermodynamics and magnetic properties of a Bose-Einstein condensate and production of a Fermi sea. Quantum Gases [cond-mat.quant-gas]. Université Sorbonne Paris Cité, 2016. English. ⟨NNT : 2016USPCD036⟩. ⟨tel-01939835⟩

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