1,720,971 research outputs found
Quantum extreme learning of molecular potential energy surfaces and force fields
Full text linkQuantum machine learning algorithms are expected to play a pivotal role in quantum chemistry simulations in the immediate future. One such key application is the training of a quantum neural network to learn the potential energy surface and force field of molecular systems. We address this task by using the quantum extreme learning machine paradigm. This particular supervised learning routine allows for resource-efficient training, consisting of a simple linear regression performed on a classical computer. We have tested a setup that can be used to study molecules of any dimension and is optimized for immediate use on NISQ devices with a limited number of native gates. We have applied this setup to three case studies: lithium hydride, water, and formamide, carrying out both noiseless simulations and actual implementation on IBM quantum hardware. Compared to other supervised learning routines, the proposed setup requires minimal quantum resources, making it feasible for direct implementation on quantum platforms, while still achieving a high level of predictive accuracy compared to simulations. Our encouraging results pave the way towards the future application to more complex molecules, being the proposed setup scalable
An operational definition of quantum information scrambling
Full text linkQuantum information scrambling (QIS) is a characteristic feature of several quantum systems,
ranging from black holes to quantum communication networks. While accurately quantifying QIS
is crucial to understanding many such phenomena, common approaches based on the tripartite
information have limitations due to the accessibility issues of quantum mutual information, and
do not always properly take into consideration the dependence on the encoding input basis. To
address these issues, we propose a novel and computationally efficient QIS quantifier, based on a
formulation of QIS in terms of quantum state discrimination. We show that the optimal guessing
probability, which reflects the degree of QIS induced by an isometric quantum evolution, is directly
connected to the accessible min-information, a generalized channel capacity based on conditional
min-entropy, which can be cast as a convex program and thus computed efficiently. By applying
our proposal to a range of examples with increasing complexity, we illustrate its ability to capture
the multifaceted nature of QIS in all its intricacy
Monopoles and dualities in 3d = 2 quivers
Full text linkInternational audienceSeiberg-like dualities in 2 + 1d quiver gauge theories with 4 supercharges are investigated. We consider quivers made of various combinations of classical gauge groups U(N), Sp(N), SO(N) and SU(N). Our main focus is the mapping of the supersymmetric monopole operators across the dual theories. There is a simple general rule that encodes the mapping of the monopoles upon dualizing a single node. This rule dictates the mapping of all the monopoles which are not dressed by baryonic operators. We also study more general situations involving baryons and baryon-monopoles, focussing on three examples: SU − Sp, SO − SO and SO − Sp quivers
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
On the interactions of Maxwell-like higher spins: Noether procedure for constrained gauge theories
No full textThis work deals with Higher-Spin Gauge Theories, an old branch of Relativistic Field Theory that attracted new interest in the last few years due to its role in instances of holographic dualities as well as in force of the possible role of higher-spin symmetries in clarifying the geometrical basis of String Theory.
Higher-spin interactions were long considered to be inconsistent, due to a number of no-go theorems mainly focused on S-matrix arguments and on minimal coupling to gravity in flat backgrounds. Starting from the end of the eighties, however, central results due to M. A. Vasiliev and collaborators showed how to bypass those negative conclusions and how to construct fully interacting non-linear equations of motion. Still, Vasiliev’s equations are intrinsically non-Lagrangian, thus motivating the effort of building an action principle for interacting higher-spin fields by some alternative route. In addition, recent findings points to some possible ambiguities in Vasiliev’s formulation: when some auxiliary fields needed in that context are removed infinite higher derivative corrections to the vertices apparently emerge, and the proper way to interpret them is currently under debate. A better understanding of higher-spin interactions formulated directly in terms of physical fields is certainly desirable.
These observations serve to motivate the central theme of this work: we construct cubic Lagrangian vertices for higher-spin gauge fields described at free level by a new class of Lagrangians, termed Maxwell-like, generalising the Fronsdal formulation to the case of reducible multiplets of massless particles. Our main tool is the so-called Noether procedure. The general idea is that, given a free gauge theory, one can construct the corresponding interacting theory in a perturbative way, adding vertices of increasing order (cubic, quartic and so on), while at the same time allowing for field-dependent corrections to the gauge transformation. The requirement that gauge invariance is kept at all orders fixes in principle all these quantities thus providing a sort of “bootstrap approach” to the construction of interacting gauge theories.
Our work covers three main aspects:
(1) We provide an overview on the main features of higher spin theories at free and interacting level. We review the group-theoretical definition of elementary particles in Relativistic Field Theory and indicate how to recover the Lagrangians for free massless fields in the formulation due to Fronsdal. We provide a somewhat streamlined critical discussion of some of the main no-go theorems against the possibility of interacting theories involving higher spins, such as the Weinberg theorem, trying to emphasize hypothesis and physical implications, while also highlighting the main mechanisms explored so far to the goal of evading the no-go results.
(2) We discuss our methodology by means of a detailed illustration of the Noether procedure. After a presentation of the general structure of the method, we show how to implement it for the low-spin cases of Maxwell fields (spin 1) and gravitons (spin 2). In the former case we show how to recover Yang-Mills theory by the mere requirement that a bunch of Maxwell fields interact in a way that be consistent with their free, Abelian gauge symmetry. In the latter case, starting from free massless spin 2 particles, we find the Einstein-Hilbert cubic vertex expanded around Minkowski space-time, together with the associated deformation of the gauge transformation, observing that it gives rise to the Lie derivative. The geometrical structure of the corresponding theories, such as the need for an underlying Lie algebra for spin−one massless fields and diffeomorphism invariance for interacting gravitons emerge as an outcome of the self-consistency procedure and need not be known in advance.
(3) The third section collects our original results. We apply the Noether procedure in the context of the Maxwell-like formulation for higher-spin gauge fields. Their relevant features are of two types: on the one hand, the kinetic tensor building the free Lagrangian is simpler with respect to the Fronsdal one, and one may hope that this simplicity is kept at the interacting level. In addition, the corresponding equations of motion propagate a reducible spectrum of particles, which matches the description of massless fields of arbitrary spin emerging from the tensionless limit of free open strings. Thus, for instance, Maxwell-like equations of motion for a rank−two symmetric tensor propagate a massless spin−two particle together with a massless scalar, as opposed to the Fronsdal case (corresponding for spin two to the linearised Einstein-Hilbert theory) that describes starting from the same tensor a single massless particle with spin two. The Maxwell-like cubic vertices resulting from our approach display a sizeable simplification with respect to the Fronsdal ones: while the latter involve a total of ten types of terms the former only make use of four classes of cubic contributions.
We find that the structure of the free gauge symmetry of Maxwell-like Lagrangians calls for a generalization of the Noether procedure that, to our knowledge, was not considered so far, at least in the higher-spin context. More precisely, we are led to consider the Noether method for gauge parameters subject to some constraints at the free level. These constraints may in principle enter the procedure in an algorithmic way, forcing an additional equation encoding their possible corrections order by order. For the Maxwell-like case we find indeed that such an additional equation is needed and we compute the explicit deformation of the constraint associated to every vertex involving arbitrary spins. In fact, with hindsight, one can realize that the deformation of the constraints can actually encode crucial information about the underlying geometry. We discuss in these terms the explicit example of a self-interacting rank-two Maxwell-like field (providing a bottom-up approach to Unimodular Gravity) and comment on the possibility that also Fronsdal trace constraints get similarly deformed, an option that so far was almost completely neglected.
Finally, we present a new class of couplings, containing particular combinations of the divergences of the fields, that are naturally suggested in our generalized Noether setting, and that was considered to be forbidden in previous treatments
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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