Theory of quantum phases and elementary excitations of Bose gases in optical lattices

王波涛 WANG Bo-tao, 姜颖 JIANG Ying

David Clément, Nicole Fabbri, L. Fallani +2 more

We report the Bragg spectroscopy of interacting one-dimensional Bose gases loaded in an optical lattice across the superfluid to the Mott-insulator phase transition. Elementary excitations are created with a nonzero momentum and the response of the correlated 1D gases is in the linear regime. The complexity of the strongly correlated quantum phases is directly displayed in the spectra which exhibit novel features. This work paves the way for a precise characterization of the state of correlated gases in optical lattices.

哲 小鍋

Emek Yesilada

Barbara Capogrosso-Sansone

In this dissertation I present results for lattice boson systems based on quantum Monte Carlo simulations by the Worm algorithm. Lattice bosons can be realized by ultracold gases in optical lattices and, under certain conditions, they are described by the Bose-Hubbard model. I will discuss the ground state, i.e. the phase diagram and properties of elementary excitations, as well as finite temperature thermodynamic properties of the two- and three-dimensional systems. These results provide bench-marks and guidance for experimentalists. I will also discuss the phase diagram of the one-dimensional hard-core Bose-Hubbard model with three-body interactions. The model is realized by cold polar molecules in optical lattices. The ground state presents a novel solid phase at unconventional filling, characterized by coexisting charge density wave and bond orders. Such phase has not been predicted by the preexisting mean field theory.

R. N. Bisset, P. B. Blakie, S. Stringari

Dilute quantum gases offer a controllable platform for investigating quantum liquids, such as superfluid helium, in which correlations and fluctuations are encoded in the form of a quasiparticle energy (i.e., roton-maxon) dispersion. An approach to extracting the roton-maxon spectrum of a Bose-Einstein condensate is theoretically developed: the method relies on using an external one-dimensional optical lattice that effectively controls the response of the system, giving access to its elementary excitations.