1,721,016 research outputs found
Thouless pumping and topology
Full text linkPhysicists and engineers from all around the world are constantly thinking of ways to improve the performance of conventional electronic devices by reducing the dissipated energy and to this aim recently is working its way employing quantum technologies. In a conductor a direct current is usually associated with a dissipative flow of electrons in response to an applied bias voltage. In quantum systems, however, a dissipationless transport can be induced via adiabatic cyclic variation of the system parameters in the absence of any external bias. An example is the quantum pump, or Thouless pump, the quantum version of the famous Archimede’s screw in which water from a low-level is pushed up the tube by the slow and periodic rotation of the helicoid. The quantum device is obtained slowly time periodic potential. Interestingly, the charge pumped after a period is quantized and is connected to a bulk property of the system, the so called topological invariant, i.e. a property of a geometric shape that does not change when the shape is stretched or distorted and thus is robust to external perturbations.
The exciting developments in the exploitation of quantum pumps have been reported in an article of the prestigious journal Nature Reviews Physics involving the Department of Physics at University of Salerno, where a research on quantum devices is coordinated by Prof. Roberta Citro, and the Quantum Optics group at Ludwig Maximilian University of Munich, led by Prof. Monika Aidelsburger. The article describes in details various quantum pumps, arguing how they produce a lot less heat than conventional electric currents generators, making them promising candidates for future electronic devices with significantly reduced power consumption.
Quantum pumping has received much attention in mesoscopic electronic systems, mainly owing to its potential of reducing the dissipation of energy as wasteful heat, for defining a better current standard for metrological purpose or even being used for quantum computing. Recent experimental realizations of Thouless pumps have been observed in photonics, magneto-mechanical and electro-mechanical systems and other examples cover the fields of spintronics with implications in the efficiency of data storage and transfer
Methods for detecting charge fractionalization and winding numbers in an interacting fermionic ladder
No full textWe consider a spin-1/2 fermionic ladder with spin-orbit coupling and a perpendicular magnetic field, which shares important similarities with topological superconducting wires. We fully characterize the symmetry-protected topological phase of this ladder through the identification of fractionalized edge modes and non-trivial spin winding numbers. We propose an experimental scheme to engineer such a ladder system with cold atoms in optical lattices, and we present two protocols that can be used to extract the topological signatures from density and momentum-distribution measurements. We then consider the presence of interactions and discuss the effects of a contact on-site repulsion on the topological phase. We find that such interactions could enhance the extension of the topological phase in certain parameters regimes
Coupling ultracold matter to dynamical gauge fields in optical lattices: From flux attachment to Z2 lattice gauge theories
Full text linkFrom the standard model of particle physics to strongly correlated electrons, various physical settings are formulated in terms of matter coupled to gauge fields. Quantum simulations based on ultracold atoms in optical lattices provide a promising avenue to study these complex systems and unravel the underlying many-body physics. Here, we demonstrate how quantized dynamical gauge fields can be created in mixtures of ultracold atoms in optical lattices, using a combination of coherent lattice modulation with strong interactions. Specifically, we propose implementation of Z2 lattice gauge theories coupled to matter, reminiscent of theories previously introduced in high-temperature superconductivity. We discuss a range of settings from zero-dimensional toy models to ladders featuring transitions in the gauge sector to extended two-dimensional systems. Mastering lattice gauge theories in optical lattices constitutes a new route toward the realization of strongly correlated systems, with properties dictated by an interplay of dynamical matter and gauge fields
Topological charge pumping in the interacting bosonic Rice-Mele model
Full text linkWe investigate topological charge pumping in a system of interacting bosons in the tight-binding limit, described by the Rice-Mele model. An appropriate topological invarient for the many-body case is the change of polarization per pump cycle, which we compute for various interaction strengths from infinite-size matrix-product-state simulations. We verify that the charge pumping remains quantized as long as the pump cycle avoids the superfluid phase. In the limit of hardcore bosons, the quantized pumped charge can be understood from single-particle properties such as the integrated Berry curvature constructed from Bloch stated, while this picture breaks down at finite interaction strengths. These two properties-robust quantized charge transport in an interacting system of bosons and breakdown of a single-particle invarient-could both be measured with ultracold quantum gases extending a previous experiment [Lohse et al., Nat. Phys. 12, 350 (2016)]. Furthermore, we investigate the entanglement spectrum of the Rice-Mele modal and argue that the quantized charge pumping is encoded in a winding of the spectral flow in the entanglement over a pump cycle
Floquet approach to Z2 lattice gauge theories with ultracold atoms in optical lattices
No full textQuantum simulation has the potential to investigate gauge theories in strongly interacting regimes, which are currently inaccessible through conventional numerical techniques. Here, we take a first step in this direction by implementing a Floquet-based method for studying Z2 lattice gauge theories using two-component ultracold atoms in a double-well potential. For resonant periodic driving at the on-site interaction strength and an appropriate choice of the modulation parameters, the effective Floquet Hamiltonian exhibits Z2 symmetry. We study the dynamics of the system for different initial states and critically contrast the observed evolution with a theoretical analysis of the full time-dependent Hamiltonian of the periodically driven lattice model. We reveal challenges that arise due to symmetry-breaking terms and outline potential pathways to overcome these limitations. Our results provide important insights for future studies of lattice gauge theories based on Floquet techniques
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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