15,718 research outputs found
Distilling common randomness from bipartite quantum states
The problem of converting noisy quantum correlations between two parties into
noiseless classical ones using a limited amount of one-way classical
communication is addressed. A single-letter formula for the optimal trade-off
between the extracted common randomness and classical communication rate is
obtained for the special case of classical-quantum correlations. The resulting
curve is intimately related to the quantum compression with classical side
information trade-off curve of Hayden, Jozsa and Winter. For a general
initial state we obtain a similar result, with a single-letter formula, when we
impose a tensor product restriction on the measurements performed by the
sender; without this restriction the trade-off is given by the regularization
of this function. Of particular interest is a quantity we call ``distillable
common randomness'' of a state: the maximum overhead of the common randomness
over the one-way classical communication if the latter is unbounded. It is an
operational measure of (total) correlation in a quantum state. For
classical-quantum correlations it is given by the Holevo mutual information of
its associated ensemble, for pure states it is the entropy of entanglement. In
general, it is given by an optimization problem over measurements and
regularization; for the case of separable states we show that this can be
single-letterized.Comment: 22 pages, LaTe
Relating quantum privacy and quantum coherence: an operational approach
We describe how to achieve optimal entanglement generation and one-way
entanglement distillation rates by coherent implementation of a class of secret
key generation and secret key distillation protocols, respectively.
This short paper is a high-level descrioption of our detailed papers [8] and
[10].Comment: 4 pages, revtex
A Resource Framework for Quantum Shannon Theory
Quantum Shannon theory is loosely defined as a collection of coding theorems,
such as classical and quantum source compression, noisy channel coding
theorems, entanglement distillation, etc., which characterize asymptotic
properties of quantum and classical channels and states. In this paper we
advocate a unified approach to an important class of problems in quantum
Shannon theory, consisting of those that are bipartite, unidirectional and
memoryless.
We formalize two principles that have long been tacitly understood. First, we
describe how the Church of the larger Hilbert space allows us to move flexibly
between states, channels, ensembles and their purifications. Second, we
introduce finite and asymptotic (quantum) information processing resources as
the basic objects of quantum Shannon theory and recast the protocols used in
direct coding theorems as inequalities between resources. We develop the rules
of a resource calculus which allows us to manipulate and combine resource
inequalities. This framework simplifies many coding theorem proofs and provides
structural insights into the logical dependencies among coding theorems.
We review the above-mentioned basic coding results and show how a subset of
them can be unified into a family of related resource inequalities. Finally, we
use this family to find optimal trade-off curves for all protocols involving
one noisy quantum resource and two noiseless ones.Comment: 60 page
A family of quantum protocols
We introduce two dual, purely quantum protocols: for entanglement
distillation assisted by quantum communication (``mother'' protocol) and for
entanglement assisted quantum communication (``father'' protocol). We show how
a large class of ``children'' protocols (including many previously known ones)
can be derived from the two by direct application of teleportation or
super-dense coding. Furthermore, the parent may be recovered from most of the
children protocols by making them ``coherent''. We also summarize the various
resource trade-offs these protocols give rise to.Comment: 5 pages, 1 figur
Analysis of close encounters with Ganymede and Callisto using a genetic n-body algorithm
In this work we describe a genetic algorithm which is used in order to study
orbits of minor bodies in the frames of close encounters. We find that the
algorithm in combination with standard orbital numerical integrators can be
used as a good proxy for finding typical orbits of minor bodies in close
encounters with planets and even their moons, saving a lot of computational
time compared to long-term orbital numerical integrations. Here, we study close
encounters of Centaurs with Callisto and Ganymede in particular. We also
perform n-body numerical simulations for comparison. We find typical impact
velocities to be between and for
Ganymede and between and for
Callisto.Comment: 18 pages, 3 figure
Characteristics of stress-induced defects under positive bias in high-k/InGaAs stacks
The introduction of InGaAs as a channel material for complementary metal-oxide-semiconductor technology presents major challenges in terms of the characterization of the various defects that affect the performance and reliability. Understanding the generation of defects by constant voltage stresses is crucial in terms of their concentration profiles and energy levels. In particular, we want to understand the real nature of the defects responsible for the dispersion of C-V in strong accumulation. Here, we show that the degradation under positive bias of metal/Al2O3/n-InGaAs capacitors reveals two contributions depending on the temperature that affects the C-V curves in a different way. Based on features of stressed C-V curves, it is possible to estimate the onset point of the distribution of border traps near the midgap condition. The results suggest that these defects are strongly related to the characteristics of the InGaAs substrate.Fil: Palumbo, Félix Roberto Mario. Technion - Israel Institute of Technology; Israel. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Winter, R.. Technion - Israel Institute of Technology; IsraelFil: Krylov, I.. Technion - Israel Institute of Technology; IsraelFil: Eizenberg, M.. Technion - Israel Institute of Technology; Israe
Product market competition, corporate governance and firm performance: an empirical analysis for Germany
Productivity growth has been slow in many continental European countries over the last few decades, especially in comparison with the United States. It has been argued that lack of product market competition and poor corporate governance are two of the main reasons for this phenomenon. However, predictions from theoretical models are far from unambiguous, and empirical evidence is sparse, in particular at the level of individual firms. In this paper, we aim to close this gap with an econometric analysis of firm performance in Germany. Based on a unique panel data set with detailed information on almost 400 manufacturing firms over the 1986-94 period, we find that firms operating in industries which are characterized by more intensive product market competition experience higher rates of productivity growth. We also find weak evidence for the notion that in Germany?s bank-based system of internal control, ownership concentration is harmful for productivity growth. --competition,corporate governance,productivity
Home Is Where the Heart Is: Determining “Habitual Residence” Under the Hague Convention on the Civil Aspects of International Child Abduction
Part I.A first outlines the three major divisions in habitual residence interpretation within the United States, paying particular attention to the approaches of the Ninth, Sixth, and Third Circuits. Next, Part I.B briefly addresses international trends in habitual residence interpretation among other signatory nations. After analyzing the shortcomings of each approach in Part II, Part III emphasizes a renewed emphasis on the child in all habitual residence determination
Estimating quantum chromatic numbers
We develop further the new versions of quantum chromatic numbers of graphs
introduced by the first and fourth authors. We prove that the problem of
computation of the commuting quantum chromatic number of a graph is solvable by
an SDP algorithm and describe an hierarchy of variants of the commuting quantum
chromatic number which converge to it. We introduce the tracial rank of a
graph, a parameter that gives a lower bound for the commuting quantum chromatic
number and parallels the projective rank, and prove that it is multiplicative.
We describe the tracial rank, the projective rank and the fractional chromatic
numbers in a unified manner that clarifies their connection with the commuting
quantum chromatic number, the quantum chromatic number and the classical
chromatic number, respectively. Finally, we present a new SDP algorithm that
yields a parameter larger than the Lov\'asz number and is yet a lower bound for
the tracial rank of the graph. We determine the precise value of the tracial
rank of an odd cycle.Comment: 34 pages; v2 has improved presentation based after referees'
comments, published versio
Representing suicide: Giving voice to a desire to die?
Drawing on interview and online ethnographic data from a study of suicide on the railways, this paper describes the ways in which many of the concepts, assumptions and practices of mainstream suicide prevention are challenged in the accounts of those who are planning, or have enacted, a suicide attempt. We reflect on the ethical dilemmas which can arise for researchers (and practitioners) when lived experience accounts diverge – theoretically, morally and in terms of practical implications – from present-day expert ones. In online, ‘pro-choice’ suicide discussions, people describe beliefs, attitudes, ways of thinking and acting which stand in contrast to existing professional and clinical descriptions of suicide and suicidal behaviour. Most obviously, there is often a rejection of ‘pro-life’ positions, which are framed as ideological, oppressive and naïve. For researchers engaging in online ethnography of ‘pro-choice’ spaces, dilemmas can arise in relation to the representation of perspectives which fundamentally challenge not only prevailing norms within suicide research and prevention practice but socio-cultural norms more widely. Similar issues can arise when considering how best to represent research participants when their accounts diverge from accepted ‘expert’ knowledge and beliefs. In-depth qualitative interviews with those who have thought about or attempted to take their own life indicate that existing theories and models of suicide which start from assumptions of deficit and pathology underestimate the extent to which suicide, as the end result of an often-complex series of actions, requires a person to engage in logistical processes of planning, decision-making, imagination and adaptation. The accounts described here, gathered using two different methodological approaches, highlight the ethical issues which can surface when there are competing claims to (expert) knowledge, as well as differences in beliefs, attitudes and moral stance towards life and death. We argue that researchers need to reflect on their own ethical-moral position in relation to suicide, and on the practical consequences of their privileging of some voices at the expense of other, less well represented, ones
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