1,720,958 research outputs found
Quantum estimation through a bottleneck
No full textWe study the estimation of a single parameter characterizing families of unitary transformations acting on two systems. We consider the situation with the presence of bottleneck, i.e., only one of the systems can be measured to gather information. The estimation capabilities are related to unitaries’ generators. In particular, we establish continuity of quantum Fisher information with respect to generators. Furthermore, we find conditions on the generators to achieve the same maximum quantum Fisher information we would have in the absence of bottleneck. We also discuss the usefulness of initial entanglement across the two systems as well as across multiple estimation instances
Discriminating qubit amplitude damping channels
Full text linkWe address the issue of the discrimination between two-qubit amplitude damping channels by exploring several strategies. For the single-shot, we show that the excited state does not always give the optimal input, and that side entanglement assistance has limited benefit. On the contrary, feedback assistance from the environment is more beneficial. For the two-shot, we prove the in-utility of entangled inputs. Then focusing on individual (local) measurements, we find the optimal adaptive strategy
Discrimination of dephasing channels
Full text linkThe problem of dephasing channel discrimination is addressed for
finite-dimensional systems. In particular, the optimization with respect to
input states without energy constraint is solved analytically for qubit, qutrit
and ququart. Additionally, it is shown that resorting to side entanglement
assisted strategy is completely useless in this case
Profitable entanglement for channel discrimination
Full text linkWe investigate the usefulness of side entanglement in discriminating between
two generic qubit channels, {\ up to unitary pre- and post-processing,} and
determine exact conditions under which it does enhance (as well as conditions
under which it does not) the success probability. This is done in a
constructive way by first analyzing the problem for channels that are extremal
in the set of completely positive and trace-preserving qubit linear maps and
then for channels that are inside such a set
Quantum reading of quantum information
Full text linkWe extend the notion of quantum reading to the case where the information to
be retrieved, which is encoded into a set of quantum channels, is of quantum
nature. We use two qubit unitaries describing the system environment
interaction, with the initial environment state determining the system's input
output channel and hence the encoded information. The performance of the most
relevant two-qubit unitaries is determined with two different approaches: i)
one-shot quantum capacity of the channel arising between environment and
system's output; ii) estimation of parameters characterizing the initial
quantum state of the environment. The obtained results are mostly in
(qualitative) agreement, with some distinguishing features that include the
CNOT unitary.Comment: Relations/differences with respect to previous works are better
explained, and new references are adde
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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