1,720,970 research outputs found
Modulational Instabilities in Lattices with Power-Law Hoppings and Interactions
No full textWe study the occurrence of modulational instabilities in lattices with nonlocal power-law hoppings and interactions. Choosing as a case study the discrete nonlinear Schrodinger equation, we consider one-dimensional chains with power-law decaying interactions (with exponent alpha) and hoppings (with exponent beta): An extensive energy is obtained for alpha,beta > 1. We show that the effect of power-law interactions is that of shifting the onset of the modulational instabilities region for alpha > 1. At a critical value of the interaction strength, the modulational stable region shrinks to zero. Similar results are found for effectively short-range nonlocal hoppings (beta > 2): At variance, for longer-ranged hoppings (1 < beta < 2) there is no longer any modulational stability. The hopping instability arises for q = 0 perturbations, thus the system is most sensitive to the perturbations of the order of the system size. We also discuss the stability regions in the presence of the interplay between competing interactions - (e. g., attractive local and repulsive nonlocal interactions). We find that noncompeting nonlocal interactions give rise to a modulational instability emerging for a perturbing wave vector q = pi while competing nonlocal interactions may induce a modulational instability for a perturbing wave vector 0 < q < pi. Since for alpha > 1 and beta > 2 the effects are similar to the effect produced on the stability phase diagram by finite range interactions and/or hoppings, we conclude that the modulational instability is "genuinely" long-ranged for 1 < beta < 2 nonlocal hoppings
Excitations and stability of weakly interacting Bose gases with multibody interactions
No full textWe consider weakly interacting bosonic gases with local and nonlocal multibody interactions. By using the Bogoliubov approximation, we first investigate contact interactions, studying the case in which the interparticle potential can be written as a sum of N-body δ interactions and then considering general contact potentials. Results for the quasiparticle spectrum and the stability are presented. We then examine nonlocal interactions, focusing on two different cases of three-body nonlocal interactions. Our results are used for systems with two- and three-body δ interactions and applied for realistic values of the trap parameters. Finally, the effect of conservative three-body terms in dipolar systems and soft-core potentials (that can be simulated with Rydberg dressed atoms) is also studied
Soliton trains after interaction quenches in Bose mixtures
Full text linkWe investigate the quench dynamics of a two-component Bose mixture and study the onset of modulational instability, which leads the system far from equilibrium. Analogous to the single-component counterpart, this phenomenon results in the creation of trains of bright solitons. We provide an analytical estimate of the number of solitons at long times after the quench for each of the two components based on the most unstable mode of the Bogoliubov spectrum, which agrees well with our simulations for quenches to the weak attractive regime when the two components possess equal intraspecies interactions and loss rates. We also explain the significantly different soliton dynamics in a realistic experimental homonuclear potassium mixture in terms of different intraspecies interaction and loss rates. We investigate the quench dynamics of the particle number of each component estimating the characteristic time for the appearance of modulational instability for a variety of interaction strengths and loss rates. Finally we evaluate the influence of the beyond-mean-field contribution, which is crucial for the ground-state properties of the mixture, in the quench dynamics for both the evolution of the particle number and the radial width of the mixture. In particular, even for quenches to strongly attractive effective interactions we do not observe the dynamical formation of solitonic droplets
Bound state dynamics in the long-range spin- 1⁄2 XXZ model
Full text linkExperimental platforms based on trapped ions, cold molecules, and Rydberg atoms have made possible the investigation of highly nonlocal spin-1/2 Hamiltonians with long-range couplings. Here, we study the effects of such nonlocal couplings in the long-range spin-1/2 XXZ Heisenberg Hamiltonian. We calculate explicitly the two-spin energy spectrum, which describes all possible energetic configurations of two spins pointing in a specific direction embedded in a background of spins with opposite orientation. For fast decay of the spin-spin couplings, we find that the two-spin energy spectrum is characterized by well-defined discrete values, corresponding to bound states, separated by a set of continuum states describing the scattering region. In the deep long-range regime instead, the bound states disappear as they get incorporated by the scattering region. The presence of two-spin bound states results to be crucial to determine both two- and many-spin dynamics. On one hand, radically different two-spin spreadings can be observed by tuning the decay of the spin couplings. On the other hand, two-spin bound states enable the dynamical stabilization of effective antiferromagnetic states in the presence of ferromagnetic couplings. Finally, we propose a novel scheme based on a trapped-ion quantum simulator to experimentally realize the long-range XXZ model and to study its out-of-equilibrium properties
Struttura della comunità macrobentonica dello Scoglio delle Sirene (Scilla, Mar Tirreno)
No full textDimensionality-enhanced quantum state transfer in long-range-interacting spin systems
No full textIn this work we study the single-qubit quantum state transfer in uniform long-range spin XXZ systems in high-dimensional geometries. We consider prototypical long-range spin exchanges that are relevant for experiments in cold atomic platforms: Coulomb, dipolar, and van der Waals-like interactions. We find that in all these cases the fidelity increases with the dimensionality of the lattice. We also find a pronounced enhancement of the fidelity in one-dimensional lattices for increasing interaction range. This can be related to the emergence of a pair of bilocalized states on the sender and receiver site due to the onset of an effective weak-coupling Hamiltonian. Finally, we test our predictions in the presence of temperature-induced disorder introducing a model for the thermal displacement of the lattice sites, considered as a set of local adiabatic oscillators
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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