1,720,959 research outputs found
Quantum correlations of identical particles subject to classical environmental noise
No full textAbstract In this work, we propose a measure for the quantum discord of indistinguishable
particles, based on the definition of entanglement of particles given in
Wiseman and Vaccaro (Phys Rev Lett 91:097902, 2003. doi:10.1103/PhysRevLett.91.
097902). This discord of particles is then used to evaluate the quantum correlations in
a system of two identical bosons (fermions), where the particles perform a quantum
random walk described by the Hubbard Hamiltonian in a 1D lattice. The dynamics of
the particles is either unperturbed or subject to a classical environmental noise—such
as random telegraph, pink or brown noise. The observed results are consistent with
those for the entanglement of particles, and we observe that on-site interaction between
particles have an important protective effect on correlations against the decoherence
of the system
Analytical expression of genuine tripartite quantum discord for symmetrical X-states
No full textThe study of classical and quantum correlations in bipartite and multipartite
systems is crucial for the development of quantum information theory. Among
the quantifiers adopted in tripartite systems, the genuine tripartite quantum discord
(GTQD), estimating the amount of quantum correlations shared among all the subsystems,
plays a key role since it represents the natural extension of quantum discord used
in bipartite systems. In this paper, we derive an analytical expression of GTQD for
three-qubit systems characterized by a subclass of symmetrical X-states. Our approach
has been tested on both GHZ and maximally mixed states reproducing the expected
results. Furthermore, we believe that the procedure here developed constitutes a valid
guideline to investigate quantum correlations in form of discord in more general multipartite
systems
Time-dependent simulation and analytical modelling of electronic Mach-Zehnder interferometry with edge-states wave packets
No full textWe compute the exact single-particle time-resolved dynamics of electronic Mach–Zehnder
interferometers based on Landau edge-states transport, and assess the effect of the spatial
localization of carriers on the interference pattern. The exact carrier dynamics is obtained by
solving numerically the time-dependent Schrödinger equation with a suitable 2D potential
profile reproducing the interferometer design. An external magnetic field, driving the system
to the quantum Hall regime with filling factor one, is included. The injected carriers are
represented by a superposition of edge states, and their interference pattern—controlled
via magnetic field and/or area variation—reproduces the one of (Ji et al 2003 Nature 422
415). By tuning the system towards different regimes, we find two additional features in the
transmission spectra, both related to carrier localization, namely a damping of the Aharonov–
Bohm oscillations with increasing difference in the arms length, and an increased mean
transmission that we trace to the energy-dependent transmittance of quantum point contacts.
Finally, we present an analytical model, also accounting for the finite spatial dispersion of the
carriers, able to reproduce the above effects
Time-dependent modelling of single-electron interferometry with edge-states
No full textWe simulate the time-resolved dynamics of localized electrons in a 2DEG system,
where an external magnetic eld creates quantum Hall edge states, and properly polarized split
gates dene a Mach-Zehnder electron interferometer. The carriers travelling inside the Hall
channels consist of localized wave packets of edge states: they are propagated numerically by
means of a Fourier split-step approach. We find that the energy-dependent scattering process at
the quantum point contacts, together with the nite energy distribution of the carriers, have a
remarkable eect on the transmission coecient T of the device. We provide an analytical model
to justify the characteristics of T which is in good agreement with the numerical simulations
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
Probing the sign of the Hubbard interaction by two-particle quantum walks
Full text linkWe address the discrimination between attractive and repulsive interaction in systems made of two identical bosons propagating on a one-dimensional lattice, and suggest a probing scheme exploiting the dynamical properties of the corresponding two-particle quantum walks. In particular, we show that the sign of the interaction leaves a clear signature in the dynamics of the two walkers, which is governed by the Hubbard model, and in their quantum correlations, thus permitting one to discriminate between the two cases. We also prove that these features are strictly connected to the band structure of the Hubbard Hamiltonian
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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