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Search Results: 1 - 10 of 223828 matches for " R. Laforest "
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Time-reversal formalism applied to maximal bipartite entanglement: Theoretical and experimental exploration
M. Laforest,J. Baugh,R. Laflamme
Physics , 2005, DOI: 10.1103/PhysRevA.73.032323
Abstract: Within the context of quantum teleportation, a proposed intuitive model to explain bipartite entanglement describes the scheme as being the same qubit of information evolving along and against the flow of time of an external observer. We investigate the physicality of such a model by applying the time-reversal of the Schrodinger equation in the teleportation context. To do so, we first lay down the theory of time-reversal applied to the circuit model and then show that the outcome of a teleportation-like circuit is consistent with the usual tensor product treatment, thus independent of the physical quantum system used to encode the information. Finally, we demonstrate a proof of principle experiment on a liquid state NMR quantum information processor. The experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement.
Randomized benchmarking of single and multi-qubit control in liquid-state NMR quantum information processing
C. A. Ryan,M. Laforest,R. Laflamme
Physics , 2008, DOI: 10.1088/1367-2630/11/1/013034
Abstract: Being able to quantify the level of coherent control in a proposed device implementing a quantum information processor (QIP) is an important task for both comparing different devices and assessing a device's prospects with regards to achieving fault-tolerant quantum control. We implement in a liquid-state nuclear magnetic resonance QIP the randomized benchmarking protocol presented by Knill et al (PRA 77: 012307 (2008)). We report an error per randomized $\frac{\pi}{2}$ pulse of $1.3 \pm 0.1 \times 10^{-4}$ with a single qubit QIP and show an experimentally relevant error model where the randomized benchmarking gives a signature fidelity decay which is not possible to interpret as a single error per gate. We explore and experimentally investigate multi-qubit extensions of this protocol and report an average error rate for one and two qubit gates of $4.7 \pm 0.3 \times 10^{-3}$ for a three qubit QIP. We estimate that these error rates are still not decoherence limited and thus can be improved with modifications to the control hardware and software.
A Combinatorial Analysis of Tree-Like Sentences  [PDF]
Gilbert Labelle, Louise Laforest
Open Journal of Discrete Mathematics (OJDM) , 2015, DOI: 10.4236/ojdm.2015.53004
Abstract: A sentence over a finite alphabet A, is a finite sequence of non-empty words over A. More generally, we define a graphical sentence over A by attaching a non-empty word over A to each arrow and each loop of a connected directed graph (digraph, for short). Each word is written according to the direction of its corresponding arrow or loop. Graphical sentences can be used to encode sets of sentences in a compact way: the readable sentences of a graphical sentence being the sentences corresponding to directed paths in the digraph. We apply combinatorial equations on enriched trees and rooted trees, in the context of combinatorial species and Pólya theories, to analyze parameters in classes of tree-like sentences. These are graphical sentences constructed on tree-like digraphs.
Robust Quantum Communication Using A Polarization-Entangled Photon Pair
J. -C. Boileau,R. Laflamme,M. Laforest,C. R. Myers
Physics , 2004, DOI: 10.1103/PhysRevLett.93.220501
Abstract: Noise and imperfection of realistic devices are major obstacles for implementing quantum cryptography. In particular birefringence in optical fibers leads to decoherence of qubits encoded in polarization of photon. We show how to overcome this problem by doing single qubit quantum communication without a shared spatial reference frame and precise timing. Quantum information will be encoded in pair of photons using ``tag'' operations which corresponds to the time delay of one of the polarization modes. This method is robust against the phase instability of the interferometers despite the use of time-bins. Moreover synchronized clocks are not required in the ideal situation no photon loss case as they are only necessary to label the different encoded qubits.
Neonatal maternal separation alters development of the hypercapnic ventilatory response in awake adult rats
Genest SE,Gulemetova R,Laforest S,Drolet G
Respiratory Research , 2001, DOI: 10.1186/rr139
Experimental Implementation of Discrete Time Quantum Random Walk on an NMR Quantum Information Processor
C. A. Ryan,M. Laforest,J. C. Boileau,R. Laflamme
Physics , 2005, DOI: 10.1103/PhysRevA.72.062317
Abstract: We present an experimental implementation of the coined discrete time quantum walk on a square using a three qubit liquid state nuclear magnetic resonance (NMR) quantum information processor (QIP). Contrary to its classical counterpart, we observe complete interference after certain steps and a periodicity in the evolution. Complete state tomography has been performed for each of the eight steps making a full period. The results have extremely high fidelity with the expected states and show clearly the effects of quantum interference in the walk. We also show and discuss the importance of choosing a molecule with a natural Hamiltonian well suited to NMR QIP by implementing the same algorithm on a second molecule. Finally, we show experimentally that decoherence after each step makes the statistics of the quantum walk tend to that of the classical random walk.
La banlieue dans l’imaginaire québécois. Problèmes originels et avenir critique
Daniel Laforest
Temps Zéro : Revue d'étude des écritures Contemporaines , 2013,
Abstract: La banlieue est l’objet d’une visibilité accrue dans l’imaginaire littéraire du Québec contemporain. Rien n’indique cependant qu’elle ait dépassé le stade de la caricature ou de la critique unidimensionnelle. Face à cela cet article formule deux hypothèses. La première est qu’il y a une ville consensuelle dans les imaginaires du Québec moderne, et que cette ville repose sur la suppression de l’historicité des formes périurbaines. La seconde est que la réhabilitation de cette historicité dégagera des avenues critiques neuves pour la lecture des récits urbains contemporains. à travers Nègres blancs d’Amérique de Pierre Vallières et Le ciel de Bay City de Catherine Mavrikakis, on verra que le mot banlieue recouvre en fait deux notions qu’il est urgent d’articuler avec le développement de la littérature québécoise : l’urbanisation et la vie ordinaire.The suburb has become progressively more visible in the literary imaginary of contemporary Québec, though nothing seems to indicate that it has surpassed the stage of caricature or unidimensional criticism. In light of this situation, two hypotheses are formulated in this article. The first is that a widely accepted type of city dominates in the imaginary of modern Québec, and that this city is founded upon the suppression of the historicity of peri-urban forms. The second is that the rehabilitation of this suppressed historicity will open new critical avenues for the interpretation of contemporary urban stories. Through an analysis of Pierre Vallières’ Nègres blancs d’Amérique and Catherine Mavrikakis’ Le ciel de Bay City, we will see that the word ‘suburb’ encompasses two notions urgently requiring clarification in view of the development of Québécois literature: urbanisation and ordinary life.
Guy Laforest
Revista d'Estudis Autonòmics i Federals , 2010,
Abstract: Ever since the federal founding of Canada in 1867, Québec has substantiallycontributed to the various stages in the evolution of the Canadian state and inthe interpretation of Canadian federalism. In the aftermath of the referendumsof 1980 and 1995, and considering that a third sovereignty referendum appearsquite unlikely in Québec, this article provides a survey and critical understandingof current federalist thinking and current academic discourses concerning federalismin Québec. Although the article is mostly about intellectual history, it integratescurrent political developments in the province of Québec, governed bythe Liberals led by Jean Charest since 2003, and in Canada as a whole as well,governed since 2006 by consecutive Conservative minority governments underthe leadership of Stephen Harper. The article shows that in the major academicdiscipines of constitutional law, history, political science and philosophy, Québecinterpretations of Canadian federalism continue to be dominated by a paradigmformulated by the Report of the Tremblay Commission, a forum for enquiry onconstitutional matters created by the Québec government more than fifty yearsago. The dominant paradigm continues to propose an existential approachfocusing on greater autonomy and recognition for Québec, while at the sametime adopting an instrumental-utilitarian stance towards Canada. While thisapproach continues to be developed with great academic sophistication, in mostof these disciplines a certain federalist revival is under way, attempting topropose a better equilibrium between the requirements of autonomy-recognitionfor Québec and those of solidarity-interdependence with the whole of Canada.
Liquid State NMR as a Test-bed for Developing Quantum Control Methods
C. A. Ryan,C. Negrevergne,M. Laforest,E. Knill,R. Laflamme
Physics , 2008, DOI: 10.1103/PhysRevA.78.012328
Abstract: In building a quantum information processor (QIP), the challenge is to coherently control a large quantum system well enough to perform an arbitrary quantum algorithm and to be able to correct errors induced by decoherence. Nuclear magnetic resonance (NMR) QIPs offer an excellent test-bed on which to develop and benchmark tools and techniques to control quantum systems. Two main issues to consider when designing control methods are accuracy and efficiency, for which two complementary approaches have been developed so far to control qubit registers with liquid-state NMR methods. The first applies optimal control theory to numerically optimize the control fields to implement unitary operations on low dimensional systems with high fidelity. The second technique is based on the efficient optimization of a sequence of imperfect control elements so that implementation of a full quantum algorithm is possible while minimizing error accumulation. This article summarizes our work in implementing both of these methods. Furthermore, we show that taken together, they form a basis to design quantum-control methods for a block-architecture QIP so that large system size is not a barrier to implementing optimal control techniques.
Using error correction to determine the noise model
M. Laforest,D. Simon,J. -C. Boileau,J. Baugh,M. Ditty,R. Laflamme
Physics , 2006, DOI: 10.1103/PhysRevA.75.012331
Abstract: Quantum error correcting codes have been shown to have the ability of making quantum information resilient against noise. Here we show that we can use quantum error correcting codes as diagnostics to characterise noise. The experiment is based on a three-bit quantum error correcting code carried out on a three-qubit nuclear magnetic resonance (NMR) quantum information processor. Utilizing both engineered and natural noise, the degree of correlations present in the noise affecting a two-qubit subsystem was determined. We measured a correlation factor of c=0.5+/-0.2 using the error correction protocol, and c=0.3+/-0.2 using a standard NMR technique based on coherence pathway selection. Although the error correction method demands precise control, the results demonstrate that the required precision is achievable in the liquid-state NMR setting.
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