85 research outputs found
Quantum discord from system-environment correlations
In an initially uncorrelated mixed separable bi-partite system, quantum
correlations can emerge under the action of a local measurement or local noise
[A. Streltsov, H. Kampermann, and D. Bru\ss{}, Phys. Rev. Lett. 107, 170502
(2011)]. We analyze this counter-intuitive phenomenon using quantum discord as
a quantifier. We then relate changes in quantum discord to system-environment
correlations between the system in a mixed state and some purifying
environmental mode using the Koashi-Winter inequality. On this basis, we
suggest an interpretation of discord as a byproduct of transferring
entanglement and correlations around the different subsystems of a global pure
state.Comment: 6 pages, submitted to the special issue of Physica Scripta on CEWQO
201
Sâauto Ă©valuer pour agir : rĂŽle du sentiment dâefficacitĂ© personnelle dans les pratiques dâenseignement
Dans son quotidien, lâenseignant est amenĂ© Ă prendre des dĂ©cisions, Ă©valuer les Ă©lĂ©ments favorables du contexte, mobiliser des ressources afin dâorganiser lâactivitĂ© pĂ©dagogique. Lâensemble de ces choix tactiques ou stratĂ©giques est sous-tendu par un processus dâauto-Ă©valuation de son action que nous avons souhaitĂ© analyser. Au sein du collĂšge les enseignants vivent en direct la nĂ©cessaire adaptation de leur projet pĂ©dagogique Ă la spĂ©cificitĂ© des Ă©lĂšves et Ă la diffĂ©renciation de leurs actes. Ces enseignants, entre deux rives, ont au quotidien Ă la fois, Ă conduire leur activitĂ©, Ă auto Ă©valuer celle-ci et Ă construire des pratiques efficaces. Notre recherche nous permet de dĂ©crire et dâexpliquer le rĂŽle des processus internes dâauto-Ă©valuation des actions professionnelles. Ces procĂ©dures sont en interaction avec la construction chez lâenseignant dâun sentiment dâauto-efficacitĂ© qui, au-delĂ de renforcer lâestime de soi, est un vĂ©ritable moteur de la valorisation et de la production des actes dâenseignement.<br>In their day to day work, teachers are required to make decisions, evaluate the positive elements in their environment and mobilize resources in order to organize their pedagogical activity. All of these tactical or strategic choices are underlain by a self-evaluation process of their action that we have chosen to analyze. In junior high school, teachers get to see how it is necessary to adapt their pedagogical projects to studentsâ specificity and to differentiated acts. Daily, these teachers have, at the same time, to conduct their activity, to self-evaluate it and to conceive efficient practices. This study enables us to better describe and explain the role of internal self-assessment processes of professional actions. These self-evaluation processes interact with the building of a sense of efficiency that, beyond strengthening teachersâ self-esteem, is a true engine of development and production of acts of education
Nonclassical correlations in continuous-variable non-Gaussian Werner states
We study nonclassical correlations beyond entanglement in a family of
two-mode non-Gaussian states which represent the continuous-variable
counterpart of two-qubit Werner states. We evaluate quantum discord and other
quantumness measures obtaining exact analytical results in special instances,
and upper and lower bounds in the general case. Non-Gaussian measurements such
as photon counting are in general necessary to solve the optimization in the
definition of quantum discord, whereas Gaussian measurements are strictly
suboptimal for the considered states. The gap between Gaussian and optimal
non-Gaussian conditional entropy is found to be proportional to a measure of
non-Gaussianity in the regime of low squeezing, for a subclass of
continuous-variable Werner states. We further study an example of a
non-Gaussian state which is positive under partial transposition, and whose
nonclassical correlations stay finite and small even for infinite squeezing.
Our results pave the way to a systematic exploration of the interplay between
nonclassicality and non-Gaussianity in continuous-variable systems, in order to
gain a deeper understanding of -and to draw a bigger advantage from- these two
important resources for quantum technology.Comment: References added, typos correcte
Measurement-induced disturbances and nonclassical correlations of Gaussian states
We study quantum correlations beyond entanglement in two-mode Gaussian states
of continuous variable systems, by means of the measurement-induced disturbance
(MID) and its ameliorated version (AMID). In analogy with the recent studies of
the Gaussian quantum discord, we define a Gaussian AMID by constraining the
optimization to all bi-local Gaussian positive operator valued measurements. We
solve the optimization explicitly for relevant families of states, including
squeezed thermal states. Remarkably, we find that there is a finite subset of
two-mode Gaussian states, comprising pure states, where non-Gaussian
measurements such as photon counting are globally optimal for the AMID and
realize a strictly smaller state disturbance compared to the best Gaussian
measurements. However, for the majority of two--mode Gaussian states the
unoptimized MID provides a loose overestimation of the actual content of
quantum correlations, as evidenced by its comparison with Gaussian discord.
This feature displays strong similarity with the case of two qubits. Upper and
lower bounds for the Gaussian AMID at fixed Gaussian discord are identified. We
further present a comparison between Gaussian AMID and Gaussian entanglement of
formation, and classify families of two-mode states in terms of their Gaussian
AMID, Gaussian discord, and Gaussian entanglement of formation. Our findings
provide a further confirmation of the genuinely quantum nature of general
Gaussian states, yet they reveal that non-Gaussian measurements can play a
crucial role for the optimized extraction and potential exploitation of
classical and nonclassical correlations in Gaussian states.Comment: 16 pages, 5 figures; new results added; to appear in Phys. Rev.
Recommended from our members
Are practical recommendations practiced? A national multi-centre cross-sectional study on frequency of visual field testing in glaucoma
Aim: To estimate current clinical practice for frequency of visual field (VF) monitoring in glaucoma in England.
Methods: A cross-sectional review of all patients with chronic open angle glaucoma (COAG) attending specialist glaucoma clinics at six hospitals in England was performed. The number of VF tests undertaken prior to the study date and during the first 2 years since diagnosis were recorded and compared with European Glaucoma Society (EGS) guidelines for newly-diagnosed patients. Clinician-requested monitoring intervals were compared with intervals from the National Institute of Clinical Excellence (NICE) guidelines, and the relationships with disease severity, intraocular pressure (IOP) and glaucoma progression status were reviewed.
Results: One-hundred and four patients with COAG were included. 73 patients had at least 2 years of follow-up. Median (IQR) total number of VF tests and in the first 2 years of diagnosis were 4 (2â7) and 2 (2â3), respectively. No patients met EGS guidelines, but 87% of patients had their monitoring intervals requested in accordance with NICE guidelines. These intervals were not related to disease severity or VF stability (KruskalâWallis test, p=0.25) but shortened significantly when IOP control was inadequate or when the overall clinical impression was disease progression (p<0.001).
Conclusions Most newly-diagnosed COAG patients receive less than three VFs in the first 2 years following diagnosis and an average of 0.7 VF per year over the duration of follow-up
Ubiquitin C-terminal hydrolases cleave isopeptide- and peptide-linked ubiquitin from structured proteins but do not edit ubiquitin homopolymers
Logistic support provided to Australian disaster medical assistance teams: results of a national survey of team members
Background: It is likely that calls for disaster medical assistance teams (DMATs) continue in response to international disasters. As part of a national survey, the present study was designed to evaluate the Australian DMAT experience and the need for logistic support.\ud
\ud
Methods: Data were collected via an anonymous mailed survey distributed via State and Territory representatives on the Australian Health Protection Committee, who identified team members associated with Australian DMAT deployments from the 2004 Asian Tsunami disaster.\ud
\ud
Results: The response rate for this survey was 50% (59/118). Most of the personnel had deployed to the South East Asian Tsunami affected areas. The DMAT members had significant clinical and international experience. There was unanimous support for dedicated logistic support with 80% (47/59) strongly agreeing. Only one respondent (2%) disagreed with teams being self sufficient for a minimum of 72 hours. Most felt that transport around the site was not a problem (59%; 35/59), however, 34% (20/59) felt that transport to the site itself was problematic. Only 37% (22/59) felt that pre-deployment information was accurate. Communication with local health providers and other agencies was felt to be adequate by 53% (31/59) and 47% (28/59) respectively, while only 28% (17/59) felt that documentation methods were easy to use and reliable. Less than half (47%; 28/59) felt that equipment could be moved easily between areas by team members and 37% (22/59) that packaging enabled materials to be found easily. The maximum safe container weight was felt to be between 20 and 40 kg by 58% (34/59).\ud
\ud
Conclusions: This study emphasises the importance of dedicated logistic support for DMAT and the need for teams to be self sufficient for a minimum period of 72 hours. There is a need for accurate pre deployment information to guide resource prioritisation with clearly labelled pre packaging to assist access on site. Container weights should be restricted to between 20 and 40 kg, which would assist transport around the site, while transport to the site was seen as problematic. There was also support for training of all team members in use of basic equipment such as communications equipment, tents and shelters and water purification systems
Australia\u27s health 2002 : the eighth biennial report of the Australian Institute of Health and Welfare
Australia\u27s Health 2002 is the eighth biennial health report of the Australian Institute of Health and Welfare. It is the nation\u27s authoritative source of information on patterns of health and illness, determinants of health, the supply and use of health services, and health service costs and performance. Australia\u27s Health 2002 is an essential reference and information resource for all Australians with an interest in health
- âŠ