The cost of exactly simulating quantum entanglement with classical communication

We investigate the amount of communication that must augment classical local hidden variable models in order to simulate the behaviour of entangled quantum systems. We consider the scenario where a bipartite measurement is given from a set of possibilities and the goal is to obtain exactly the same correlations that arise when the actual quantum system is measured. We show that, in the case of a single pair of qubits in a Bell state, a constant number of bits of communication is always sufficient--regardless of the number of measurements under consideration. We also show that, in the case of a system of n Bell states, a constant times 2^n bits of communication are necessary.Comment: 9 pages, LaTeX, no figure

Quantum Amplitude Amplification and Estimation

Consider a Boolean function $\chi: X \to \{0,1\}$ that partitions set $X$ between its good and bad elements, where $x$ is good if $\chi(x)=1$ and bad otherwise. Consider also a quantum algorithm $\mathcal A$ such that $A |0\rangle= \sum_{x\in X} \alpha_x |x\rangle$ is a quantum superposition of the elements of $X$, and let $a$ denote the probability that a good element is produced if $A |0\rangle$ is measured. If we repeat the process of running $A$, measuring the output, and using $\chi$ to check the validity of the result, we shall expect to repeat $1/a$ times on the average before a solution is found. *Amplitude amplification* is a process that allows to find a good $x$ after an expected number of applications of $A$ and its inverse which is proportional to $1/\sqrt{a}$, assuming algorithm $A$ makes no measurements. This is a generalization of Grover's searching algorithm in which $A$ was restricted to producing an equal superposition of all members of $X$ and we had a promise that a single $x$ existed such that $\chi(x)=1$. Our algorithm works whether or not the value of $a$ is known ahead of time. In case the value of $a$ is known, we can find a good $x$ after a number of applications of $A$ and its inverse which is proportional to $1/\sqrt{a}$ even in the worst case. We show that this quadratic speedup can also be obtained for a large family of search problems for which good classical heuristics exist. Finally, as our main result, we combine ideas from Grover's and Shor's quantum algorithms to perform amplitude estimation, a process that allows to estimate the value of $a$. We apply amplitude estimation to the problem of *approximate counting*, in which we wish to estimate the number of $x\in X$ such that $\chi(x)=1$. We obtain optimal quantum algorithms in a variety of settings.Comment: 32 pages, no figure

A patient with anti-NXP2-positive dermatomyositis and syphilis

Dermatomyositis is an auto-immune inflammatory myopathy that primarily affects the skin and muscle and can be triggered by exposure to various environmental factors. We present a patient with active syphilis infection who developed dermatomyositis and discuss the significance of anti-NXP2 autoantibody positivity

A limit on nonlocality in any world in which communication complexity is not trivial

Bell proved that quantum entanglement enables two space-like separated parties to exhibit classically impossible correlations. Even though these correlations are stronger than anything classically achievable, they cannot be harnessed to make instantaneous (faster than light) communication possible. Yet, Popescu and Rohrlich have shown that even stronger correlations can be defined, under which instantaneous communication remains impossible. This raises the question: Why are the correlations achievable by quantum mechanics not maximal among those that preserve causality? We give a partial answer to this question by showing that slightly stronger correlations would result in a world in which communication complexity becomes trivial.Comment: 13 pages, no figure

La gestion des Activités éducatives de la direction et le fonctionnement de l'école primaire

Many actors in the field of education assert that principals should pay closer attention to educational activities in order to ensure students' achievement. This paper presents a research conducted with 138 principals and 421 teachers which aimed at assessing the frequency of principals' interventions on managing educational activities in elementary schools in Quebec. In addition, this study examines the relations between principals' management of educational activities and the different aspect of the school's functioning. The results show that principals intervene more frequently in specific areas of management such as parents' involvement and the support of at-risk students rather than the supervision of teachers and students' performance. Hence, the quality of the school's functioning varies in the nature and frequency of the principal's intervention which illustrates the importance of their managerial work.Key words:    management of educational activities, educational leadership, school's functioning, students' achievement

Detection of Hepatitis E virus in swine using real-time RT-PCR

The zoonotic transmtsswn potential of Hepatitis E virus (HEY) is now widely recognized. Swine represents the main animal reservoir for this virus in many countries, including Canada. In recent years, different real-time RT-PCR assays were developed and proposed as reliable and sensitive detection methods. However, the quality of extracted RNA, presence of inhibitors and RN ase contamination of the samples may impact on the detection results obtained with these molecular methods. The aim of this study was to evaluate the use of a sample process control (SPC) within a real-time RT-PCR assay for the detection ofHEV. This TaqMan multiplex assay was afterwards used to evaluate the viral load ofHEV in organs, tissues and excreta of normal pigs at slaughter. HEY RNA was detected in at least one sample from 14 out of the 43 animals tested (32.6 %). HEV was present in lymph nodes (25.6%), bladder (23.3%), liver (20.9%), bile (18.6%), feces (13.9%), tonsils (7.0%) and plasma (2.3%) but was undetected in loins