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Investigation of the Mott transition with metastable Helium atoms

Cécile Carcy 1
1 Laboratoire Charles Fabry / Gaz Quantiques
LCF - Laboratoire Charles Fabry
Abstract : In this work, we transfer a Bose-Einstein condensate of metastable Helium atoms to a 3D cubic lattice potential (optical lattice). This system is an experimental realization of the Bose-Hubbard Hamiltonian that depends on two parameters that are the interaction strength U between the atoms and the kinetic energy J. Depending on the value of the ratio U/J, the ground state of the system is either a superfluid (SF) or a Mott insulator (MI). In the experiment, we investigated the Mott transition that separates the SF and the MI phases. Thanks to the use of He$^*$ atoms, one can detect the atoms individually and in 3D after a long time-of-flight. As a result, we access the in-trap momentum distribution of the lattice gases probed with a single atom sensitivity and one can compute the momentum correlations at any order. We demonstrate that the 2 and 3-particles correlations of a Mott insulator deep in the MI phase are the ones of a system described by a gaussian density operator. In the MI phase, we investigate the restoration of the first-order coherence on approaching the Mott transition. Finally, by comparing the momentum distributions measured in the experiment with Quantum Monte Carlo numerical simulations performed with the experimental parameters and calculated for a wide range of temperatures, we calculated the temperature of the lattice gases probed, allowing us to investigate the transition between a SF and a thermal gas (NF) that occurs when increasing the temperature of the system. We notably have measured the condensate fraction across the SF-NF and the SF-MI transitions. We demonstrated that when probing trapped systems, if the condensate fraction is a good observable to locate the position of the phase transition, it is not the case for the SF-MI transition. We thus probed different observables.
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  • HAL Id : tel-02890916, version 2

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Cécile Carcy. Investigation of the Mott transition with metastable Helium atoms. Optics [physics.optics]. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLO014⟩. ⟨tel-02890916v2⟩

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