Magnetic phase transition in coherently coupled Bose gases in optical lattices

We describe the ground state of a gas of bosonic atoms with two coherently coupled internal levels in a deep optical lattice in a one dimensional geometry. In the single-band approximation this system is described by a Bose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating phase which can be either paramagnetic or ferromagnetic. We characterize the quantum phase transitions at unit filling by means of a density matrix renormalization group technique and compare it with a mean-field approach. The presence of the ferromagnetic Ising-like transition modifies the Mott lobes. In the Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ model in a transverse field and the numerical results compare very well with the analytical results obtained from the spin model. In the superfluid regime quantum fluctuations strongly modify the phase transition with respect to the well established mean-field three dimensional classical bifurcation.Comment: 6 pages, 3 figure

Bogoliubov Theory of acoustic Hawking radiation in Bose-Einstein Condensates

We apply the microscopic Bogoliubov theory of dilute Bose-Einstein condensates to analyze quantum and thermal fluctuations in a flowing atomic condensate in the presence of a sonic horizon. For the simplest case of a step-like horizon, closed-form analytical expressions are found for the spectral distribution of the analog Hawking radiation and for the density correlation function. The peculiar long-distance density correlations that appear as a consequence of the Hawking emission features turns out to be reinforced by a finite initial temperature of the condensate. The analytical results are in good quantitative agreement with first principle numerical calculations.Comment: 11 pages, 7 figure

Dipolar Drag in Bilayer Harmonically Trapped Gases

We consider two separated pancake-shaped trapped gases interacting with a dipolar (either magnetic or electric) force. We study how the center of mass motion propagates from one cloud to the other as a consequence of the long-range nature of the interaction. The corresponding dynamics is fixed by the frequency difference between the in-phase and the out-of-phase center of mass modes of the two clouds, whose dependence on the dipolar interaction strength and the cloud separation is explicitly investigated. We discuss Fermi gases in the degenerate as well as in the classical limit and comment on the case of Bose-Einsten condensed gases.Comment: Submitted to EPJD, EuroQUAM special issue "Cold Quantum Matter - Achievements and Prospects

Out-of-equilibrium states and quasi-many-body localization in polar lattice gases

The absence of energy dissipation leads to an intriguing out-of-equilibrium dynamics for ultracold polar gases in optical lattices, characterized by the formation of dynamically-bound on-site and inter-site clusters of two or more particles, and by an effective blockade repulsion. These effects combined with the controlled preparation of initial states available in cold gases experiments can be employed to create interesting out-of-equilibrium states. These include quasi-equilibrated effectively repulsive 1D gases for attractive dipolar interactions and dynamically-bound crystals. Furthermore, non-equilibrium polar lattice gases can offer a promising scenario for the study of many-body localization in the absence of quenched disorder. This fascinating out-of-equilibrium dynamics for ultra-cold polar gases in optical lattices may be accessible in on-going experiments.Comment: 5+1 pages, 4+1 figure