Séminaire de Physique Théorique

Ultracold Interacting Bosons: Quantum Magnetism and Beyond
Laurent de Forges (Université de Fribourg-en-Brisgau, Allemagne)
Thursday 15 March 2018 14:00 -  Tours -  Salle 1180 (Bât E2)

Résumé :
The use of ultracold atoms as quantum simulators allows the study of strongly interacting quantum systems. These systems allow to explore the physics of well-known discrete quantum statistical scenarios such as the Bose-Hubbard model. The pioneering experiments by M. Greiner et al. [1], which allows for the direct observation of the quantum phase transition from a superfluid to a Mott insulator state, has definitely opened a novel area of research: Since 16 years, a huge amount of researchers, including me, is motivated by the observation of new quantum phases and phase transitions. In particular, recent progress in the field have allowed the study of bosonic systems with multiple components, such as bosons with spin degree of freedom and atomic-molecular mixtures. The richness of these systems comes from the competition between different terms of the extended Bose-Hubbard Hamiltonian, leading to multicomponent Bose-Einstein condensates, multiple transitions and quantum magnetism. Two systems particularly drew my attention: an atomic and molecular mixtures [2], and a model of spin-1 atoms with spin-spin interactions [3]. Employing a combined strategy based on exact numerical methods (quantum Monte Carlo simulations and exact diagonalization) and analytical calculations, we have derived the phase diagrams and characterized the phase transitions beyond the mean field description. I will show that these systems exhibit intriguing phases (e.g. nematic order, Feshbach Insulator and mixed superfluidity), as well as many quantum phase transitions (XY, Ising, BKT, and singlet-to-nematic). [1] M. Greiner et al., Nature 415, 39-44 (2002). [2] L. de Forges de Parny et al., PRL 114, 195302 (2015). [3] L. de Forges de Parny et al., PRL 113, 200402 (2014).

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