Search

I argue that scientific determinism is not supported by facts, but results from the elegance of the mathematical language physicists use, in particular from the so-called real numbers and their infinite series of digits. Classical physics can thus be interpreted in a deterministic or indeterministic way. However, using quantum physics, some experiments prove that nature is able to continually produce new information, hence support indeterminism in physics., Comment: Original version in French, to appear in the proceedings of the "Colloque Exp\'erience et V\'erit\'e(s)" organized by the faculty of theology, Geneva University, September 3-4 2023

The theory of probability and the quantum theory, the one mathematical and the other physical, are related in that each admits a number of very different interpretations. It has been proposed that the conceptual problems of the quantum theory could be, if not resolved, at least mitigated by a proper interpretation of probability. We rather show, through a historical and analytical overview of probability and quantum theory, that if some interpretations of the one and the other go along particularly well, none follows in a unique way., Comment: English version of a semitechnical paper published in French in RQS

All investigators working on the foundations of quantum mechanics agree that the theory has profoundly modified our conception of reality. But there ends the consensus. The unproblematic formalism of the theory gives rise to a number of very different interpretations, each of which has consequences on the notion of reality. This paper analyses how the Copenhagen interpretation, von Neumann's state vector collapse, Bohm and de Broglie's pilot wave and Everett's many worlds modify, each in its own way, the classical conception of reality, whose local character, in particular, requires revision., Comment: In French; contribution to a celebration of Mario Bunge's 100th birthday; forthcoming in Metascience

Quantum resource theories allow us to quantify a useful quantum phenomenon, to develop new protocols for its detection and determine the exact processes that maximize its use for practical tasks. These theories aim at transforming physical phenomena, such as entanglement and quantum coherence, into useful properties for the execution of concrete tasks related to quantum information. In this thesis, we focus on the resource theories of entanglement, discord-like quantum correlations, and quantum coherence, the most intriguing quantum phenomena exploited so far in quantum information theory. We begin by presenting in detail the theoretical tools of these quantum resources, focusing on the most remarkable techniques and computational problems. In this sense, we discuss several mathematical methods that solve some problems related to their quantifications, and some analytical results for bipartite quantum systems are given. We also examine the intrinsic connections between these quantum resources by extracting the links that unite the corresponding measures. In contrast, the revolution of quantum technology has led to a growing interest in quantum metrology, and quantum entanglement has been employed to overcome the classical limit in several quantum estimation protocols. In this work, we analyze the role of quantum correlations beyond entanglement in improving the accuracy of an unknown parameter. According to our results, correlations can be captured using quantum Fisher information, and quantum discord correlations can be exploited to ensure the accuracy of phase estimation protocols. This thesis includes also the contributions on the dynamics of these quantum resources in various models of open quantum systems. Among our objectives, is to study the effects of the environment on these quantum resources and to obtain techniques to protect them from the effects of intrinsic decoherence., Comment: PhD Dissertation, in French language. Successfully defended on September 11, 2021

We argue that Anton Zeilinger's "foundational conceptual principle" for quantum mechanics according to which an elementary system carries one bit of information is an idealistic principle, which should be replaced by a realistic principle of contextuality. Specific properties of quantum systems are a consequence of impossibility to speak about them without reference to the tools of their observation (identification) and, consequently, context in which these tools are applied. In particular, the assumption of non-locality is not required to explain quantum correlation. Correlated quantum events are related with each other in a causal way. But this is not classical, but quantum causality expressed by an entangled wave function. This or that particular correlation does not arise in measurement; in measurement it is identified in context. In contrast to Zeilinger's proposed principle of quantization of information, the principle of contextuality explains it realistically., Comment: 7 pages, in French

In this paper, after some recalls about connectivity structures and about the formalisms of quantum mechanics, we associate some families of connectivity structures with any entangled quantum state, and with any "measurement device" on such states. This finally allows us to define a new classification tool for quantum entanglement: the connectivity order. --- Dans ce texte, apr\`es des rappels d'une part sur la notion de structure connective et d'autre part sur les formalismes de la m\'ecanique quantique, nous associons certaines familles de structures connectives \`a tout \'etat quantique intriquant un nombre fini quelconque de particules, ainsi qu'\`a tout "dispositif de mesure", portant sur de tels \'etats. Cela nous permet finalement de d\'efinir un nouvel outil de classification de l'intrication quantique : l'ordre connectif., Comment: in French. 46 pages, avec index des notations et table des mati\`eres. Deux figures

In the paradigm with a small warped Spacelike Extra Dimensions (SED), the Higgs field is in general localized at a boundary of the SED (TeV-brane) where the gravity scale is redshifted to the TeV by a warp factor. If the SM gauge bosons and fermions propagate into the warped SED, one can generate the mass hierarchy for fermions. It is thus crucial to treat carefully the TeV-brane localized masses for such fermions, which is done in the literature by applying a regularization process suffering from a lack of consistency and more importantly being useless, as we demonstrate in detail in the present thesis. The first part of the thesis is devoted to the treatment of brane localized mass terms for 5D fermions, which requires the introduction of new Lagrangian terms at the SED boundaries, similar to the Gibbons-Hawking terms in gravity. The second part consists in applying different methods (function/distribution fields, 4D/5D calculations, etc) to various brane localized terms (kinetic terms, Majorana masses, etc), as well as a generalization to several classified models (flat/warped dimensions, intervalle/orbifold, etc). In the third part, we propose to compactify a flat SED on a star/rose graph with a large number of identical small leaves/petals. We obtain a compactified space with a large volume without a large compactification length to stabilize. We use the approach of 5D fermions to build a toy model of small Dirac neutrino masses (brane localized left-handed neutrinos and bulk right-handed ones)., Comment: 244 pages. PhD thesis manuscript. Part I "State of the Art" in French and Part II "Original Research Work" in English

The notion of contextuality, which emerges from a theorem established by Simon Kochen and Ernst Specker (1960-1967) and by John Bell (1964-1966), is certainly one of the most fundamental aspects of quantum weirdness. If it is a questioning on scholastic philosophy and a study of contrafactual logic that led Specker to his demonstration with Kochen, it was a criticism of von Neumann's "proof" that led John Bell to the result. A misinterpretation of this famous "proof" will lead them to diametrically opposite conclusions. Over the last decades, remarkable theoretical progresses have been made on the subject in the context of the study of quantum foundations and quantum information. Thus, the graphic generalizations of Cabello-Severini-Winter and Acin-Fritz-Leverrier-Sainz raise the question of the connection between non-locality and contextuality. It is also the case of the sheaf-theoretic approach of Samson Abramsky et al., which also invites us to compare contextuality with the logical structure of certain classical logical paradoxes. Another approach, initiated by Robert Spekkens, generalizes the concept to any type of experimental procedure. This new form of "universal" contextuality has been raised as a criterion of non-classicality, i.e. of weirdness. It notably led to identify the nature of curious quantum paradoxes involving post-selections and weak measurements. In the light of the fiftieth anniversary of the publication of the Kochen-Specker theorem, this report aims to introduce these results little known to the French scientific public, in the context of an investigation on the nature of the weirdness of quantum physics., Comment: 193 pages, 61 figures, Written in French

La m\'ecanique quantique est une th\'eorie physique contemporaine r\'eput\'ee pour ses d\'efis au sens commun et ses paradoxes. Depuis bient\^ot un si\`ecle, plusieurs interpr\'etations de la th\'eorie ont \'et\'e propos\'ees par les physiciens et les philosophes, offrant des images quantiques du monde, ou des m\'etaphysiques, radicalement diff\'erentes. L'existence d'un hasard fondamental, ou d'une multitude de mondes en-dehors du n\^otre, d\'epend ainsi de l'interpr\'etation adopt\'ee. Cet article, en s'appuyant sur le livre Boyer-Kassem (2015), Qu'est-ce que la m\'ecanique quantique ?, pr\'esente trois principales interpr\'etations quantiques, empiriquement \'equivalentes : l'interpr\'etation dite orthodoxe, l'interpr\'etation de Bohm, et l'interpr\'etation des mondes multiples. Quantum mechanics is a contemporary physical theory which is famous for its paradoxes. For about a century, several interpretations of the theory have been proposed by physicists and philosophers, giving very different images of the world, or metaphysics. For instance, whether there exists a fundamental chance, or a multiplicity of worlds, depends on the chosen interpretation. This articles relies on the book Boyer-Kassem (2015), Qu'est-ce que la m\'ecanique quantique ? (=What is quantum mechanics?), and presents three main quantum interpretations, that are empirically equivalent: the so-called orthodox interpretation, Bohmian mechanics, and the many-worlds interpretation., Comment: in French, 8 pages. Implications Philosophiques, 2015

Quantum computers facing chaos. Quantum parallelism allows to perform computation in a radically new manner. A quantum computer based on these new principles may resolve certain problems exponentially faster than a classical computer. We discuss how quantum computers can simulate complex dynamics, in particularly the dynamics of chaotic systems, where the errors of classical computation grow exponentially fast. ----- Le parallelisme autorise par la mecanique quantique permet d'effectuer des calculs d'une maniere radicalement nouvelle. Un ordinateur quantique fonde sur ces principes pourrait resoudre certains problemes exponentiellement plus vite qu'un ordinateur classique. Nous discutons comment un ordinateur quantique realiste peut simuler une dynamique complexe, en particulier les systemes chaotiques ou les fautes de l'ordinateur classique croissent exponentiellement vite., Comment: in French, 7 pages, 4 figures, revue a paraitre dans Images de la Physique, recherches faites a Quantware MIPS Center http://www.quantware.ups-tlse.fr

Einstein's reply to Weyl about the importance in General Relativity of the identity of the sources of spectral lines is well know. We show that, already in Special Relavitity, Einstein's definition of the unit of time from the frequency of atomic emission is deeply incompatible with Poincare's classical conception of time in his special relativity based on the duality "true time-local time". By using Weisskopf's analysis of quantum nature of the identity of atoms, we show that the concept of identity is implicit in Einstein's principle of relativity. On the contrary, in Poincare's relativistic logic, the use of the Lorentz transformations compensates the differences (contraction of lengths and dilation of durations) that are real by principle. The borderline "quantum-classical" passes therefore clearly between the two conceptions of the clocks in special relativity., Comment: 27 pages, 2 figures, 2 appendixes, talk given (in French)in "L'institut Henri Poincare", Paris, March 2000

Project of an undergraduate student in physics (4th year) about the concept of quantum computers (QC) and its social impact. After a thourough theoretical introduction (chap. 2), the recent debate about NMR-based QC is dealt with in detail (chap. 3). Chapter 4 comments on the figure of the number of articles published on the subject, showing the dramatic growth after the publication of Shor's algorithm., Comment: 30 pages, 1 figures; in French; Projet STS (Science, Technique et Societe). Comments Welcome