On the power of non-local boxes

A non-local box is a virtual device that has the following property: given that Alice inputs a bit at her end of the device and that Bob does likewise, it produces two bits, one at Alice's end and one at Bob's end, such that the XOR of the outputs is equal to the AND of the inputs. This box, inspired from the CHSH inequality, was first proposed by Popescu and Rohrlich to examine the question: given that a maximally entangled pair of qubits is non-local, why is it not maximally non-local? We believe that understanding the power of this box will yield insight into the non-locality of quantum mechanics. It was shown recently by Cerf, Gisin, Massar and Popescu, that this imaginary device is able to simulate correlations from any measurement on a singlet state. Here, we show that the non-local box can in fact do much more: through the simulation of the magic square pseudo-telepathy game and the Mermin-GHZ pseudo-telepathy game, we show that the non-local box can simulate quantum correlations that no entangled pair of qubits can in a bipartite scenario and even in a multi-party scenario. Finally we show that a single non-local box cannot simulate all quantum correlations and propose a generalization for a multi-party non-local box. In particular, we show quantum correlations whose simulation requires an exponential amount of non-local boxes, in the number of maximally entangled qubit pairs.Comment: 14 pages, 1 figur

No nonlocal box is universal

We show that standard nonlocal boxes, also known as Popescu-Rohrlich machines, are not sufficient to simulate any nonlocal correlations that do not allow signalling. This was known in the multipartite scenario, but we extend the result to the bipartite case. We then generalize this result further by showing that no finite set containing any finite-output-alphabet nonlocal boxes can be a universal set for nonlocality.Comment: Additions to the acknowledgements sectio

Les déterminants de l'efficacité collective des enseignants et de la performance organisationnelle en milieu scolaire collégial

PAREA n°PA-2013-016La présente recherche a été subventionnée par le ministère de l’Éducation, de l’Enseignement supérieur et de la Recherche dans le cadre du Programme d’aide à la recherche sur l’enseignement et l’apprentissage (PAREA).Comprend des références bibliographique

« Notre efficacité collective au cœur de notre organisation du travail » - 388 profs de cégeps

Affiche présentée dans le cadre du Colloque de l'ARC, «Des racines et des ailes pour la recherche collégiale», dans le cadre du 85e Congrès de l’Acfas, Université McGill, Montréal, les 8 et 9 mai 2017.L’efficacité collective des professeurs est reconnue comme un facteur clé de la réussite étudiante. Décrite comme étant la croyance qu’ont les membres d’un groupe de pouvoir performer ensemble en tant que système, elle est analysée ici selon deux dimensions : le déploiement de stratégies d’enseignement (DSE) et la gestion de classe (GC). Malgré l’intérêt à l’égard de l’efficacité collective, peu d’études ont validé ses déterminants et ses manifestations. La présente recherche examine trois déterminants - sentiment d’autoefficacité (SE), collaboration (COL) et structure administrative (SA) - et trois manifestations - épuisement émotionnel (EE), engagement organisationnel (EO) et performance organisationnelle (PO) - de l’efficacité collective. La population de l’étude transversale est de 388 enseignants (62,1 % femmes; Mâge=42,37) provenant de neuf établissements québécois d’enseignement collégial (taux de réponse : 15,1 %). Les analyses de régression montrent que le SE (β=0,31) joue un plus grand rôle quant au DSE que la COL (β=0,18) et la SA (β=0,15) ainsi qu’envers la GC (SE : β=0,29; COL : β=0,22; SA : β=0,13). Le modèle explique 7 % de la variance de l’EO et 9 % de celle de la PO, où seule la GC participe à l’explication (respectivement β=0,23; β=0,21). Dans le cadre de la communication, d’autres facteurs pouvant contribuer à l’efficacité collective, dont le leadership transformationnel, la confiance envers la direction et les conditions de travail seront présentés

Can one see entanglement ?

The human eye can detect optical signals containing only a few photons. We investigate the possibility to demonstrate entanglement with such biological detectors. While one person could not detect entanglement by simply observing photons, we discuss the possibility for several observers to demonstrate entanglement in a Bell-type experiment, in which standard detectors are replaced by human eyes. Using a toy model for biological detectors that captures their main characteristic, namely a detection threshold, we show that Bell inequalities can be violated, thus demonstrating entanglement. Remarkably, when the response function of the detector is close to a step function, quantum non-locality can be demonstrated without any further assumptions. For smoother response functions, as for the human eye, post-selection is required.Comment: 5 pages, 5 figure

Multipartite fully-nonlocal quantum states

We present a general method to characterize the quantum correlations obtained after local measurements on multipartite systems. Sufficient conditions for a quantum system to be fully-nonlocal according to a given partition, as well as being (genuinely) multipartite fully-nonlocal, are derived. These conditions allow us to identify all completely-connected graph states as multipartite fully-nonlocal quantum states. Moreover, we show that this feature can also be observed in mixed states: the tensor product of five copies of the Smolin state, a biseparable and bound entangled state, is multipartite fully-nonlocal.Comment: 5 pages, 1 figure. Version published in PRA. Note that it does not contain all the results from the previous version; these will be included in a later, more general, pape

Maximal violation of the I3322 inequality using infinite dimensional quantum systems

The I3322 inequality is the simplest bipartite two-outcome Bell inequality beyond the Clauser-Horne-Shimony-Holt (CHSH) inequality, consisting of three two-outcome measurements per party. In case of the CHSH inequality the maximal quantum violation can already be attained with local two-dimensional quantum systems, however, there is no such evidence for the I3322 inequality. In this paper a family of measurement operators and states is given which enables us to attain the largest possible quantum value in an infinite dimensional Hilbert space. Further, it is conjectured that our construction is optimal in the sense that measuring finite dimensional quantum systems is not enough to achieve the true quantum maximum. We also describe an efficient iterative algorithm for computing quantum maximum of an arbitrary two-outcome Bell inequality in any given Hilbert space dimension. This algorithm played a key role to obtain our results for the I3322 inequality, and we also applied it to improve on our previous results concerning the maximum quantum violation of several bipartite two-outcome Bell inequalities with up to five settings per party.Comment: 9 pages, 3 figures, 1 tabl