14 research outputs found

    Fractional-filling Mott domains in two dimensional optical superlattices

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    Ultracold bosons in optical superlattices are expected to exhibit fractional-filling insulating phases for sufficiently large repulsive interactions. On strictly 1D systems, the exact mapping between hard-core bosons and free spinless fermions shows that any periodic modulation in the lattice parameters causes the presence of fractional-filling insulator domains. Here, we focus on two recently proposed realistic 2D structures where such mapping does not hold, i.e. the two-leg ladder and the trimerized kagome' lattice. Based on a cell strong-coupling perturbation technique, we provide quantitatively satisfactory phase diagrams for these structures, and give estimates for the occurrence of the fractional-filling insulator domains in terms of the inter-cell/intra-cell hopping amplitude ratio.Comment: 4 pages, 3 figure

    Engineering many-body quantum dynamics by disorder

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    Going beyond the currently investigated regimes in experiments on quantum transport of ultracold atoms in disordered potentials, we predict a crossover between regular and quantum-chaotic dynamics when varying the strength of disorder. Our spectral approach is based on the Bose-Hubbard model describing interacting atoms in deep random potentials. The predicted crossover from localized to diffusive dynamics depends on the simultaneous presence of interactions and disorder, and can be verified in the laboratory by monitoring the evolution of typical experimental initial states.Comment: 4 pages, 4 figures (improved version), to be published in PR

    Dynamical bifurcation as a semiclassical counterpart of a quantum phase transition

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    We illustrate how dynamical transitions in nonlinear semiclassical models can be recognized as phase transitions in the corresponding -- inherently linear -- quantum model, where, in a Statistical Mechanics framework, the thermodynamic limit is realized by letting the particle population go to infinity at fixed size. We focus on lattice bosons described by the Bose-Hubbard (BH) model and Discrete Self-Trapping (DST) equations at the quantum and semiclassical level, respectively. After showing that the gaussianity of the quantum ground states is broken at the phase transition, we evaluate finite populations effects introducing a suitable scaling hypothesis; we work out the exact value of the critical exponents and we provide numerical evidences confirming our hypothesis. Our analytical results rely on a general scheme obtained from a large-population expansion of the eigenvalue equation of the BH model. In this approach the DST equations resurface as solutions of the zeroth-order problem.Comment: 4 pages, 3 figures; a few changes made in the layout of equations; improved visibility of some figures; added some references and endnote

    Attractive ultracold bosons in a necklace optical lattice

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    We study the ground-state properties of the Bose-Hubbard model with attractive interactions on an M-site one-dimensional periodic—necklacelike—lattice, whose experimental realization in terms of ultracold atoms is promised by a recently proposed optical trapping scheme, as well as by the control over the atomic interactions and tunneling amplitudes granted by well-established optical techniques. We compare the properties of the quantum model to a semiclassical picture based on a number-conserving su͑M͒ coherent state, which results in a set of modified discrete nonlinear Schrödinger equations. We show that, owing to the presence of a correction factor ensuing from number conservation, the ground-state solution to these equations provides a remarkably satisfactory description of its quantum counterpart not only—as expected—in the weak-interaction, superfluid regime, but even in the deeply quantum regime of large interactions and possibly small populations. In particular, we show that in this regime, the delocalized, Schrödinger-cat-like quantum ground state can be seen as a coherent quantum superposition of the localized, symmetry-breaking ground state of the variational approach. We also show that, depending on the hopping to interaction ratio, three regimes can be recognized both in the semiclassical and quantum picture of the system

    Instability Effects in the Dynamics of three Coupled Bosonic Wells

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    We report on the dynamics of three bosonic wells (trimer model) coupled cyclically and occupied by N bosons within the standard mean-field picture. Based on the identification of the fixed points of the dynamics, we find periodic solutions representing the trimer proper modes (the system behavior is discussed for initial conditions close to such states in some relevant cases) and the origin of dynamical instabilities. A diffused chaotic behavior and various macroscopic phenomena are detected numerically. Their dependence on macroscopic model parameters is evaluated as well. Finally, we consider the trimer dynamics for an open chain in the case when the central well has an adjustable depth