1,720,990 research outputs found
Topological Quantum Computation, Anyons and non-Abelian Gauge Potentials
Full text linkThis thesis deals with the study of topological quantum computation and the possible realization of non-Abelian anyons in cold atomic gases. Two main topics are investigated:
the first subject is the quantum hashing technique to approximate unitary operators by
braiding non-Abelian anyons, the second one is the analysis of systems of multicomponent
ultracold atoms in the presence of an effective non-Abelian gauge potential giving rise to a
quantum Hall regime. The common frame of these topics is the emergent study of topological
phases of matters, driven by the necessity to overcome the Landau-Ginzburg paradigm
to describe strongly correlated quantum systems such as the quantum Hall ones. To achieve
this goal it is crucial to involve seemingly distant branches of knowledge such as conformal
field theories, topological field theories, integrable models, knot theory, tensor category
theory but also quantum information and computation, in order to deepen our understanding
of the new and exciting experimental and numerical results given by the analysis of different
systems sharing these topological properties
Strange correlators for topological quantum systems from bulk-boundary correspondence
Full text link“Strange” correlators provide a tool to detect topological phases arising in many-body models by computing the matrix elements of suitably defined two-point correlations between the states under investigation and trivial reference states. Their effectiveness depends on the choice of the adopted operators. In this paper, we give a systematic procedure for this choice, discussing the advantages of choosing operators using the bulk-boundary correspondence of the systems under scrutiny. Via the scaling exponents, we directly relate the algebraic decay of the strange correlators with the scaling dimensions of gapless edge modes operators. We begin our analysis with lattice models hosting symmetry-protected topological phases and we analyze the sums of the strange correlators, pointing out that integrating their moduli substantially reduces cancellations and finite-size effects. We also analyze instances of systems hosting intrinsic topological order, as well as strange correlators between states with different nontrivial topologies. Our results for both translational and nontranslational invariant cases, and in the presence of on-site disorder and long-range couplings, extend the validity of the strange correlator approach for the diagnosis of topological phases of matter and indicate a general procedure for their optimal choice
Axial anomaly in multi-Weyl and triple-point semimetals
Full text linkWe derive the expression of the abelian axial anomaly in the so-called multi- Weyl and triple-point crossing semimetals. No simplifying restrictions are assumed on the symmetry of the spectrum. Three different computation methods are considered: the per- turbative quantum field theory procedure which is based on the evaluation of the one-loop Feynman diagrams, the Nielsen-Ninomiya method, and the Atiyah-Singer index argument. It is shown that the functional form of the axial anomaly does not depend on the Lorentz symmetry, but it is determined by the gauge structure group. We discuss the stability of the anomaly — stemming from the quantisation of the anomaly coefficient — under smooth modifications of the lagrangian parameters
Quantum Simulation of the Tricritical Ising Model in Tunable Josephson Junction Ladders
Full text linkModern hybrid superconductor-semiconductor Josephson junction arrays are a
promising platform for analog quantum simulations. Their controllable and
non-sinusoidal energy/phase relation opens the path to implement nontrivial
interactions and study the emergence of exotic quantum phase transitions. Here,
we propose the analysis of an array of hybrid Josephson junctions defining a
2-leg ladder geometry for the quantum simulation of the tricritical Ising phase
transition. This transition provides the paradigmatic example of minimal
conformal models beyond Ising criticality and its excitations are intimately
related with Fibonacci non-Abelian anyons and topological order in two
dimensions. We study this superconducting system and its thermodynamic phases
based on bosonization and matrix-product-states techniques. Its effective
continuous description in terms of a three-frequency sine-Gordon quantum field
theory suggests the presence of the targeted tricritical point and the
numerical simulations confirm this picture. Our results indicate which
experimental observables can be adopted in realistic devices to probe the
physics and the phase transitions of the model. Additionally, our proposal
provides a useful one-dimensional building block to design exotic topological
order in two-dimensional scalable Josephson junction arrays.Comment: 6 pages, 3 figures and Supplemental materia
Gauge theories with ultracold atoms
No full textWe discuss and review, in this chapter, the developing field of research of quantum simulation of gauge theories with ultracold atoms.</p
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
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