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Claude Cohen Tannoudji

Prix Nobel en 1997 pour le ralentissement et le piégeage des atomes par la lumière laser.

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Accueil du site > Séminaires > LKB > Quantum Monte Carlo Study of Superfluidity and Supersolidity in Bosonic Lattice Systems

Quantum Monte Carlo Study of Superfluidity and Supersolidity in Bosonic Lattice Systems

Exposé de Takahiro Ohgoe (Univ. of Tokyo)

Vendredi 8 février 2013, 9h15, salle de réunion du siège de l’IFRAF, au 4e étage du bâtiment Rataud à l’ENS au 45 rue d’Ulm, 75005 Paris

Abstract

In recent years, there has been great experimental development on cold atoms and molecules trapped in optical lattices. Since such a system of bosons is well described by the Bose-Hubbard model, they offer an opportunity to realize fascinating phenomena that were predicted in the simple model theoretically. Indeed, it is expected that exotic quantum phases such as supersolid phases (i.e. coexistence of superfluidity and solidity) appear in dipolar bosonic systems (ex. Cr atoms) due to the long-range interaction.

Motivated by these backgrounds, we have investigated quantum phases in the extended Bose-Hubbard models that include the effect of the long-range interaction. The method that we used is the unbiased quantum Monte Carlo method based on the worm algorithm. We first studied the Bose-Hubbard model with the nearest-neighbor interaction a square lattice and a simple cubic lattice. This model has great importance, because it is one of minimal models that support the existence of supersolid phases. The supersolid phases usually appear when particles or holes are doped into a commensurate perfect solid. However, by obtaining broad ground-state phase diagrams, we show that there is a region where supersolid appears without any doping[1,2].

Next, we have studied the Bose-Hubbard model with the dipole-dipole interaction on a square lattice. In this study, we treated the long-range interaction accurately (i.e. without any cutoff). By our simulations, we have obtained the ground-state phase diagrams for the two following cases : (i) the dipole moments are polarized parallelly to the 2D plane (hard-core bosons) and (ii) the dipole moments are polarized perpendicularly to the 2D plane (soft-core bosons). For (i), we have showed the existence of a striped solid phase, the absence of the supersolid phase, and the existence of the region where multiple plateaus are observed in the particle density[3]. For (ii), we have found a novel nested-solid phase and its supersolid phase. In particular, we show that the nested-solid structure appears through successive transitions at finite temperatures[4].

References
[1] T. Ohgoe, T, Suzuki, and N. Kawashima, Phys. Rev. Lett. 108, 185302 (2012)
[2] T. Ohgoe, T, Suzuki, and N. Kawashima, Phys. Rev. B 86, 054520 (2012)
[3] T. Ohgoe, T, Suzuki, and N. Kawashima, Phys. Rev. A 86, 063635 (2012)
[4] T. Ohgoe, T, Suzuki, and N. Kawashima, in preparation.


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