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This thesis intends to familiarize the reader with the concepts of photon statistics and correlations in quantum optics. Developing light sources that emit quantum states is central for the realization of quantum technologies. One important step in characterizing these sources is the measurement of field fluctuations and correlations, by coincidence measurements. The expectation value of a coincidence measurement, a simultaneous measurement of two intensities (or, more general, four fields), is represented by the fourth-order correlation function. The value of the correlation function, at zero delay between the detection of two photons, reveals important properties of the state to which they belonged, for example the fluctuations of the photon number. Since predictability is important for many applications, light sources emitting single photons are also characterized by the indistinguishability of consecutively emitted photons, or of two photons from separate emitters. In paper I we investigate blinking behaviour in quantum emitters, and its effect on the interference pattern and photon statistics with photons from two separate emitters. Blinking refers to an emitters transition into a non-emitting state, and subsequent transition back to an emitting state. We show that blinking can not be treated as linear loss, when measuring the fourth-order correlation function for two emitters in a Hong-Ou-Mandel setup. In general, a measurement of the fourth-order correlation function is robust to loss, which makes it a very practical tool. However, the relation between recorded coincidence counts and the correlation function is only direct in the limit of zero detection efficiency, and depends on the detection system. In paper II, we show that by adding a variable attenuation in the beam path, we can trace back to the ''true'' value of the correlation function at zero quantum efficiency. This method improves accuracy in correlation measurements by decreasing a systematic error at the expense of an increased statistical error, which is easier to handle, extending the use of coincidence methods to classical and non-classical multi-photon states. / <p>QC 20180517</p>

Metasurfaces have presented themselves as next generation optical platforms with an unprecedented capability to exert designer amplitude, phase, and polarization control on incoming electromagnetic (EM) waves. Existing works have focused on demonstrating simple optical functionalities (lensing, beam steering, holography) at longer wavelengths (microwave, infrared), and the design methodology has largely been empirical. In this work, we demonstrate next generation metasurface applications in near infrared and visible wavelengths. The purpose of such applications evolves from imaging to complex machine vision applications, and as such calls for a updated design paradigm that combines traditional, empirical based methods with modern inverse design tools based on machine learning. We expand the potential of metasurfaces by demonstrating their interdisciplinary applications in complex imaging, quantum optics and optical computation. A homebrew fabrication and testing pipeline is developed to support the challenging mission of near infrared and visible frequency usage. Furthermore, we propose a new design paradigm that combines physics informed intuitions with modern machine learning to simulate and design metasurface in an accurate and time-efficient way. In conclusion, I will discuss the outlook of metasurfaces in real-world applications, whose unique combination of performance and form factor make them ideal candidates for next-generation optical devices.

<p dir="ltr">Following the development of laser technology in the 1960s, radiation pressure was soon employed to manipulate particles by Arthur Ashkin in the 1970s. Since then, levitated optomechanics has been widely studied across physics, engineering, chemistry, and biology. In this dissertation, we first experimentally demonstrate GHz rotation and sensing with an optically levitated nanodumbbell near a surface. Then, we propose achieving optical refrigeration below liquid nitrogen temperature using near-field Purcell enhancement.</p><p dir="ltr">The first part of this dissertation focuses on fast rotation and sensing with a non-spherical silica nanoparticle levitated near a surface. Specifically, we optically levitate a nanodumbbell at 430 nm away from a surface in high vacuum and drive it to rotate at 1.6 GHz. This corresponds to a relative linear velocity of 1.4 km/s between the tip of the nanodumbbell and the surface at sub-micrometer separation. The near-surface rotating nanodumbbell demonstrates a superior torque sensitivity of (5.0 +/- 1.1 ) x 10^-26 Nm at room temperature. Our numerical simulation shows that such an ultra-sensitive nanodumbbell levitated near nanostructures can be used to detect fundamental physics, such as Casimir torque and non-Newtonian gravity. </p><p dir="ltr">In the latter part of this dissertation, we propose that optical refrigeration of solid with anti-Stokes fluorescence can be enhanced by Purcell effect. The spontaneous emission rate of high-energy photons is Purcell enhanced by coupling with a near-field cavity. The enhanced emission shifts the mean emission wavelength and enables optical refrigeration with high-absorption cooling laser. We estimate a minimum achievable temperature of 38 K with a Yb³⁺:YLiF₄ nanocrystal near a cavity using our proposed Purcell enhanced optical refrigeration method. This method can be applied to other rare-earth ion doped materials and enable applications that require solid-state cooling below liquid nitrogen temperature.</p>

Quantum memories are key components in photonics-based quantum information processing networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their very long storage times as well as their experimental simplicity and versatility. Operation with the Raman memory protocol enables high time-bandwidth products, which denote the number of possible storage trials within the memory lifetime. Since large time-bandwidth products enable multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing, the Raman memory is a promising tool for such tasks. Particularly, the broad spectral bandwidth allows for direct and technologically simple interfacing with other photonic primitives, such as heralded single photon sources. Here, this kind of light-matter interface is implemented using a warm caesium vapour Raman memory. Firstly, we study the storage of polarisation-encoded quantum information, a common standard in quantum information processing. High quality polarisation preservation for bright coherent state input signals can be achieved, when operating the Raman memory in a dual-rail configuration inside a polarisation interferometer. Secondly, heralded single photons are stored in the memory. To this end, the memory is operated on-demand by feed-forward of source heralding events, which constitutes a key technological capability for applications in temporal multiplexing. Prior to storage, single photons are produced in a waveguide-based spontaneous parametric down conversion source, whose bespoke design spectrally tailors the heralded photons to the memory acceptance bandwidth. The faithful retrieval of stored single photons is found to be currently limited by noise in the memory, with a signal-to-noise ratio of approximately 0.3 in the memory output. Nevertheless, a clear influence of the quantum nature of an input photon is observed in the retrieved light by measuring the read-out signal's photon statistics via the g⁽²⁾-autocorrelation function. Here, we find a drop in g⁽²⁾ by more than three standard deviations, from g⁽²⁾ ~ 1.69 to g⁽²⁾ ~ 1.59 upon changing the input signal from coherent states to heralded single photons. Finally, the memory noise processes and their scalings with the experimental parameters are examined in detail. Four-wave-mixing noise is determined as the sole important noise source for the Raman memory. These experimental results and their theoretical description point towards practical solutions for noise-free operation.

The processing of information based on the generation of common quantum optical states (e.g. coherent states) and the measurement of the quadrature components of the light field (e.g. homodyne detection) is often referred to as continuous-variable quantum information processing. It is a very fertile field of investigation, at a crossroads between quantum optics and information theory, with notable successes such as unconditional continuous-variable quantum teleportation or Gaussian quantum key distribution. In quantum optics, the states of the light field are conveniently characterized using a phase-space representation (e.g. Wigner function), and the common optical components effect simple affine transformations in phase space (e.g. rotations). In quantum information theory, one often needs to determine entropic characteristics of quantum states and operations, since the von Neuman entropy is the quantity at the heart of entanglement measures or channel capacities. Computing entropies of quantum optical states requires instead turning to a state-space representation of the light field, which formally is the Fock space of a bosonic mode.<p>This interplay between phase-space and state-space representations does not represent a particular problem as long as Gaussian states (e.g. coherent, squeezed, or thermal states) and Gaussian operations (e.g. beam splitters or squeezers) are concerned. Indeed, Gaussian states are fully characterized by the first- and second-order moments of mode operators, while Gaussian operations are defined via their actions on these moments. The so-called symplectic formalism can be used to treat all Gaussian transformations on Gaussian states, including mixed states of an arbitrary number of modes, and the entropies of Gaussian states are directly linked to their symplectic eigenvalues.<p>This thesis is concerned with the Gaussian transformations applied onto arbitrary states of light, in which case the symplectic formalism is unapplicable and this phase-to-state space interplay becomes highly non trivial. A first motivation to consider arbitrary (non-Gaussian) states of light results from various Gaussian no-go theorems in continuous-variable quantum information theory. For instance, universal quantum computing, quantum entanglement concentration, or quantum error correction are known to be impossible when restricted to the Gaussian realm. A second motivation comes from the fact that several fundamental quantities, such as the entanglement of formation of a Gaussian state or the communication capacity of a Gaussian channel, rely on an optimization over all states, including non-Gaussian states even though the considered state or channel is Gaussian. This thesis is therefore devoted to developing new tools in order to compute state-space properties (e.g. entropies) of transformations defined in phase-space or conversely to computing phase-space properties (e.g. mean-field amplitudes) of transformations defined in state space. Remarkably, even some basic questions such as the entanglement generation of optical squeezers or beam splitters were unsolved, which gave us a nice work-bench to investigate this interplay. <p>In the first part of this thesis (Chapter 3), we considered a recently discovered Gaussian probabilistic transformation called the noiseless optical amplifier. More specifically, this is a process enabling the amplification of a quantum state without introducing noise. As it has long been known, when amplifing a quantum signal, the arising of noise is inevitable due to the unitary evolution that governs quantum mechanics. It was recently realized, however, that one can drop the unitarity of the amplification procedure and trade it for a noiseless, albeit probabilistic (heralded) transformation. The fact that the transformation is probabilistic is mathematically reflected in the fact that it is non trace-preserving. This quantum device has gained much interest during the last years because it can be used to compensate losses in a quantum channel, for entanglement distillation, probabilistic quantum cloning, or quantum error correction. Several experimental demonstrations of this device have already been carried out. Our contribution to this topic has been to derive the action of this device on squeezed states and to prove that it acts quite surprisingly as a universal (phase-insensitive) optical squeezer, conserving the signal-to-noise ratio just as a phase-sensitive optical amplifier but for all quadratures at the same time. This also brought into surface a paradoxical effect, namely that such a device could seemingly lead to instantaneous signaling by circumventing the quantum no-cloning theorem. This paradox was discussed and resolved in our work.<p>In a second step, the action of the noiseless optical amplifier and it dual operation (i.e. heralded noiseless attenuator) on non-Gaussian states has been examined. We have observed that the mean-field amplitude may decrease in the process of noiseless amplification (or may increase in the process of noiseless attenuation), a very counterintuitive effect that Gaussian states cannot exhibit. This work illustrates the above-mentioned phase-to-state space interplay since these devices are defined as simple filtering operations in state space but inferring their action on phase-space quantities such as the mean-field amplitude is not straightforward. It also illustrates the difficulty of dealing with non-Gaussian states in Gaussian transformations (these noiseless devices are probabilistic but Gaussian). Furthermore, we have exhibited an experimental proposal that could be used to test this counterintuitive feature. The proposed set-up is feasible with current technology and robust against usual inefficiencies that occur in optical experiment. <p>Noiseless amplification and attenuation represent new important tools, which may offer interesting perspectives in quantum optical communications. Therefore, further understanding of these transformations is both of fundamental interest and important for the development and analysis of protocols exploiting these tools. Our work provides a better understanding of these transformations and reveals that the intuition based on ordinary (deterministic phase-insensitive) amplifiers and losses is not always applicable to the noiseless amplifiers and attenuators.<p>In the last part of this thesis, we have considered the entropic characterization of some of the most fundamental Gaussian transformations in quantum optics, namely a beam splitter and two-mode squeezer. A beam splitter effects a simple rotation in phase space, while a two-mode squeezer produces a Bogoliubov transformation. Thus, there is a well-known phase-space characterization in terms of symplectic transformations, but the difficulty originates from that one must return to state space in order to access quantum entropies or entanglement. This is again a hard problem, linked to the above-mentioned interplay in the reverse direction this time. As soon as non-Gaussian states are concerned, there is no way of calculating the entropy produced by such Gaussian transformations. We have investigated two novel tools in order to treat non-Gaussian states under Gaussian transformations, namely majorization theory and the replica method.<p>In Chapter 4, we have started by analyzing the entanglement generated by a beam splitter that is fed with a photon-number state, and have shown that the entanglement monotones can be neatly combined with majorization theory in this context. Majorization theory provides a preorder relation between bipartite pure quantum states, and gives a necessary and sufficient condition for the existence of a deterministic LOCC (local operations and classical communication) transformation from one state to another. We have shown that the state resulting from n photons impinging on a beam splitter majorizes the corresponding state with any larger photon number n’ > n, implying that the entanglement monotonically grows with n, as expected. In contrast, we have proven that such a seemingly simple optical component may have a rather surprising behavior when it comes to majorization theory: it does not necessarily lead to states that obey a majorization relation if one varies the transmittance (moving towards a balanced beam splitter). These results are significant for entanglement manipulation, giving rise in particular to a catalysis effect.<p>Moving forward, in Chapter 5, we took the step of introducing the replica method in quantum optics, with the goal of achieving an entropic characterization of general Gaussian operations on a bosonic quantum field. The replica method, a tool borrowed from statistical physics, can also be used to calculate the von Neumann entropy and is the last line of defense when the usual definition is not practical, which is often the case in quantum optics since the definition involves calculating the eigenvalues of some (infinite-dimensional) density matrix. With this method, the entropy produced by a two-mode squeezer (or parametric optical amplifier) with non-trivial input states has been studied. As an application, we have determined the entropy generated by amplifying a binary superposition of the vacuum and an arbitrary Fock state, which yields a surprisingly simple, yet unknown analytical expression. Finally, we have turned to the replica method in the context of field theory, and have examined the behavior of a bosonic field with finite temperature when the temperature decreases. To this end, information theoretical tools were used, such as the geometric entropy and the mutual information, and interesting connection between phase transitions and informational quantities were found. More specifically, dividing the field in two spatial regions and calculating the mutual information between these two regions, it turns out that the mutual information is non-differentiable exactly at the critical temperature for the formation of the Bose-Einstein condensate.<p>The replica method provides a new angle of attack to access quantum entropies in fundamental Gaussian bosonic transformations, that is quadratic interactions between bosonic mode operators such as Bogoliubov transformations. The difficulty of accessing entropies produced when transforming non-Gaussian states is also linked to several currently unproven entropic conjectures on Gaussian optimality in the context of bosonic channels. Notably, determining the capacity of a multiple-access or broadcast Gaussian bosonic channel is pending on being able to access entropies. We anticipate that the replica method may become an invaluable tool in order to reach a complete entropic characterization of Gaussian bosonic transformations, or perhaps even solve some of these pending conjectures on Gaussian bosonic channels.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

La physique quantique fut introduite au début du 20e siècle. Elle<p>apporte une nouvelle description du monde qui nous entoure et en<p>particulier de ce qu'on appelle le monde de l'infiniment<p>petit. Cette nouvelle théorie permet une description adéquate<p>notamment de l'effet photoélectrique, des niveaux énergétiques des<p>atomes, des réactions nucléaires, Elle apporte également une<p>réponse à de nombreuses problématiques telles que la catastrophe<p>ultraviolette. Néanmoins aussi séduisante que soit cette théorie,<p>les prédictions pour le moins contre-intuitives qu'elle apporte,<p>amène rapidement la controverse. Par exemple, en 1935, A.<p>Einstein, B. Podolski et N. Rosen en arrivent à mettre en doute la<p>physique quantique à cause d'une particularité que l'on y<p>rencontre, à savoir l'enchevêtrement. Il s'en<p>suit le célèbre débat avec N. Bohr et l'école de Copenhagen. Parmi<p>les autres aspects propres au monde quantique on peut encore citer<p>la superposition des états, le postulat de la mesure, le principe<p>d'incertitude d'Heisenberg, la dualité onde-corpuscule, le<p>théorème de non clonage, Toutes ces spécificités font de la<p>physique quantique un monde passionnant dans lequel, à l'instar du<p>pays des merveilles d'Alice, l'intuition est souvent dépassée.<p><p>Cette thèse est le fruit de quatre années de travail au cours<p>desquelles nous avons tenté d'observer et d'étudier certains des<p>effets intrigants que nous propose la physique quantique. Plus<p>précisément nous avons utilisé des états particuliers de la<p>lumière afin d'explorer une partie de ce qu'on appelle<p>l'optique quantique.<p><p>Dans un premier temps nous nous sommes intéressés aux possibilités<p>offertes par l'utilisation d'états cohérents de la lumière. En<p>utilisant ces états particuliers nous nous sommes penchés sur<p>l'étude ainsi que sur la réalisation expérimentale d'une tâche qui<p>se révèle impossible classiquement sans hypothèse computationelle.<p>Cette tâche consiste à réaliser un pile ou face entre deux joueurs<p>éloignés l'un de l'autre, par exemple deux joueurs communiquant<p>par téléphone. En effet, classiquement, un des deux joueurs pourra<p>toujours tricher de manière à avoir 100% de chance de gagner le<p>pile ou face.<p><p>Au contraire, si on utilise les ressources offertes par la<p>communication quantique, il est possible de construire des<p>protocoles ne permettant plus à aucun des deux joueurs de tricher<p>parfaitement et ce, sans aucune hypothèse supplémentaire. Même si<p>aucun protocole quantique ne peut empêcher totalement toute<p>tricherie, leur démonstration constitue une preuve de principe<p>quant aux possibilités offertes par la physique quantique dans la<p>réalisation de tâches classiquement impossibles.<p><p>Lors de notre étude du problème, nous avons développé un protocole<p>de pile ou face quantique et étudié ses performances. Nous avons<p>montré que les tentatives de tricherie des deux joueurs avaient<p>une probabilité de succès limitée à 99,7%<100% (biais inférieur<p>à 0,497). L'originalité de cette étude se situe dans le fait que<p>les imperfections expérimentales (efficacité des détecteurs,<p>pertes de transmission, visibilité réduite, ) furent prises en<p>compte, ce qui à notre connaissance n'avait jamais été réalisé. En<p>outre nous avons réalisé une implémentation en optique fibrée de<p>notre protocole et démontré la réalisation d'un pile ou face<p>unique au cours duquel aucun des deux joueurs ne pouvait<p>influencer parfaitement le résultat, ce qui à notre connaissance<p>n'avait également jamais été démontré. L'emploi d'états cohérents<p>de la lumière fortement atténués nous a donc permis de concevoir<p>un protocole de pile ou face quantique et de réaliser une<p>démonstration expérimentale en optique fibrée, d'une tâche<p>impossible à réaliser classiquement.<p><p><p>Après avoir travaillé avec des états cohérents fortement atténués,<p>nous nous sommes intéressés à un autre état quantique de la<p>lumière, à savoir les paires de photons. Ces états constituent non<p>seulement une ressource essentielle pour sonder les effets<p>quantiques de la lumière mais également une ressource<p>incontournable pour l'information et la communication quantique.<p>Nous nous sommes donc attelés à la réalisation d'une source<p>produisant ces paires de photons.<p><p> Les premières sources de paires<p>de photons furent basées sur l'utilisation de cristaux dans<p>lesquels il existe une interaction non linéaire entre la lumière<p>et le matériau du cristal. Malheureusement le désavantage majeur<p>de ces sources est la difficulté à collecter les paires de photons<p>générées. Nous avons donc étudié la possibilité de générer des<p>paires de photons directement dans une fibre optique, la<p>collection des paires y étant réalisée de facto.<p><p>La première solution que nous avons envisagée consiste à utiliser<p>la non-linéarité du troisième ordre de la silice composant les<p>fibres optiques. Plus précisément le phénomène utilisé est appelé<p>l'instabilité de modulation. Ce phénomène permet de détruire deux<p>photons de pompe afin de générer une paire de photons vérifiant<p>les conservations de l'énergie et de l'impulsion. En outre nous<p>avons choisi d'utiliser une fibre optique microstructurée. Ces<p>fibres permettent en effet un plus grand confinement de la lumière<p>que les fibres standards. Il en résulte une interaction non<p>linéaire plus importante, permettant ainsi de générer des paires<p>de photons de manière plus efficace. La fibre utilisée est en<p>outre biréfringente, ce qui permet d'avoir accès à deux types<p>particuliers d'instabilité de modulation: l'instabilité scalaire<p>et l'instabilité vectorielle.<p><p>Dans un premier temps, nous avons observé le processus<p>d'instabilité de modulation dans un régime classique. Les<p>paramètres particuliers de notre fibre microstructurée - forte<p>dispersion anormale et biréfringence modérée<p> - nous ont permis d'observer un régime<p>d'instabilité dans lequel l'instabilité de modulation vectorielle<p>se produit à des fréquences proches de la fréquence de pompe<p>($Omegasim 1$THz). Il en résulte que les bandes de gain liées à<p>l'instabilité de modulation vectorielle sont très proches des<p>bandes de gain liées à l'instabilité de modulation scalaire. Nous<p>avons observé que dans ce régime particulier, les densités<p>d'énergie générées par instabilité de modulation vectorielle sont<p>supérieures à celles générées par instabilité de modulation<p>scalaire. A notre connaissance, il s'agit de la première<p>observation expérimentale permettant de mettre en évidence un gain<p>vectoriel supérieur au gain scalaire.<p><p>La génération de paires de photons grâce à ce processus nécessite<p>de diminuer la puissance de pompe envoyée dans la fibre.<p>Malheureusement nous avons mesuré que dans ce régime de faible<p>puissance (régime quantique), la qualité des paires de photons<p>générées était fortement dégradée par la présence de photons<p>parasites générés par diffusion Raman spontanée. Nous avons estimé<p>que lorsque la puissance de pompe est abaissée suffisamment pour<p>générer en moyenne 0,1~photons dans la bande de gain d'instabilité<p>de modulation vectorielle ($sim$1543 nm), environ 75% des<p>photons détectés auront été générés par diffusion Raman spontanée.<p>Afin de mettre en oeuvre des expériences d'optique quantique<p>utilisant des paires de photons, des solutions doivent donc être<p>appliquées à notre source afin de réduire le nombre de photons<p>générés par diffusion Raman spontanée. Parmi ces solutions nous<p>pouvons citer la discrimination en polarisation des photons<p>générés ainsi que le refroidissement de la fibre grâce à de<p>l'azote liquide. Ces solutions permettraient de réduire le nombre<p>de photons Raman anti-Stokes d'un facteur 18 et le nombre de<p>photons Raman Stokes d'un facteur 4. Malheureusement la tenue de<p>la fibre microstructurée à de très basses températures reste<p>incertaine et l'implémentation de ces solutions rendrait la source<p>difficilement utilisable.<p><p><p>Notre première tentative pour générer des paires de photons dans<p>une fibre optique nous a montré que les paires de photons générées<p>grâce à un processus d'interaction non linéaire du troisième ordre<p>étaient polluées par des photons générés par diffusion Raman<p>spontanée. Une source de paires de photons efficace ne pouvait<p>donc pas être obtenue sans l'aide de solutions technologiques<p>assez lourdes à mettre en oeuvre.<p><p>Nous avons donc investigué une deuxième solution afin de réaliser<p>une source produisant des paires de photons dans une fibre<p>optique. Puisque les non-linéarités du troisième ordre semblent<p>être peu adaptées pour la génération de paires de photons, nous<p>sommes revenus à une non-linéarité du second ordre. Dans ces<p>processus c'est un photon de pompe qui est détruit afin de générer<p>une paire de photons, tout en respectant les conservations de<p>l'énergie et de l'impulsion. Malheureusement les fibres optiques<p>ne permettent pas l'apparition de non-linéarités du second ordre<p>et ce, à cause de la centrosymétrie macroscopique du verre de<p>silice qui compose ces fibres.<p><p>Afin d'induire une non-linéarité du second ordre dans une fibre<p>optique nous avons travaillé en collaboration avec l'équipe du<p>Prof. P. G. Kazansky de l'université de Southampton. En utilisant<p>les techniques de poling thermique et d'effacement par<p>illumination UV, ils réalisèrent une fibre optique twin-hole<p>périodiquement polée dans laquelle les non-linéarités du second<p>ordre furent possibles.<p><p>Grâce à cette fibre nous avons réalisé une source de paires de<p>photons combinant les avantages des effets non linéaires du second<p>ordre, i.e. la puissance de pompe nécessaire est moindre<p>que dans le cas d'une non-linéarité du troisième ordre, la<p>diffusion Raman spontanée n'influence aucunement les paires de<p>photons générées, et les avantages de la fibre optique,<p>i.e. la collection des paires de photons y est réalisée<p>de facto, le mode spatial transverse des paires de photons<p>est bien défini. La mesure du pic de coïncidences de notre source<p>fournit un rapport entre le sommet du pic et le niveau des<p>coïncidences accidentelles de 7,5. Une efficacité conversion<p>$P_s/P_p=1,2,10^{-11}$ fut obtenue en utilisant 43~mW de<p>puissance de pompe. En outre les paires de photons générées<p>possèdent une longueur d'onde de 1556~nm se trouvant ainsi dans la<p>bande C des télécommunications optiques (1530-1565~nm). Elles sont<p>donc bien adaptées à une éventuelle application en communication<p>quantique, dans les réseaux de fibres optiques actuellement<p>utilisés pour les télécommunications optiques. Enfin nous avons<p>utilisé ces paires de photons afin de réaliser l'expérience de<p>Hong-Ou-Mandel permettant de mettre en évidence un effet propre à<p>la physique quantique, à savoir le photon bunching. Une visibilité<p>nette de 40% fut obtenue pour le Mandel dip dans une<p>configuration où la visibilité maximale vaut 50%. En outre cette<p>expérience nous a permis de développer une expertise dans la<p>réalisation d'interféromètres fibrés, stabilisés et contrôlés en<p>température.<p><p><p>La source de paires de photons que nous avons réalisée constitue<p>une démonstration de principe quant à la faisabilité d'une telle<p>source. A l'époque de ce travail, la fibre dont nous disposions<p>était l'une des premières fibres twin-hole périodiquement polées.<p>Aujourd'hui de nombreux paramètres de la fibre ont été améliorés<p>et permettent la réalisation d'une source de paires de photons<p>tout à fait compétitive avec les autres sources existantes. Ainsi<p>l'équipe du Prof. Kazansky est capable de réaliser des fibres<p>périodiquement polées de 20 cm de long possédant une efficacité de<p>conversion normalisée de seconde harmonique de<p>$eta_{SH}=8;10^{-2}$\\%/W. Si l'on suppose toujours une puissance<p>de pompe de 43 mW, cela mène à une efficacité de conversion de<p>$1,0;10^{-9}$ pour le processus de fluorescence paramétrique,<p>soit une amélioration de deux ordres de grandeurs par rapport à<p>notre démonstration. La réalisation d'une source de paires de<p>photons dans une fibre optique périodiquement polée qui serait non<p>seulement utilisable dans des expériences de physique fondamentale<p>mais également dans des applications en communication quantique,<p>est donc tout à fait envisageable dans un futur proche.<p><p><p>Pour résumer, nous avons, au cours de cette thèse, réalisé, dans<p>un premier temps, la tâche classiquement impossible qui consiste à<p>jouer à pile ou face à distance. Ensuite dans l'optique de générer<p>des paires de photons, nous avons étudié le processus<p>d'instabilité de modulation dans une fibre microstructurée. Nous<p>avons ainsi observé un régime particulier dans lequel<p>l'instabilité de modulation vectorielle possède un gain supérieur<p>à celui de l'instabilité de modulation scalaire. Enfin toujours en<p>quête d'une source de paires de photons, nous avons réalisé une<p>source produisant des paires de photons par fluorescence<p>paramétrique dégénérée au sein d'une fibre optique twin-hole<p>périodiquement polée. Les trois principaux sujets abordés au cours<p>de cette thèse ont donc en commun l'utilisation de l'optique<p>fibrée pour la manipulation ou la génération d'états quantiques de<p>la lumière. Il en a résulté l'obtention de trois résultats<p>originaux qui nous ont ainsi permis d'explorer une partie du monde<p>intrigant et fascinant de l'optique quantique.<p><p>/<p><p>Quantum physics was introduced early in the 20th century. It<p>brings a whole new description of our world, mostly at the<p>microscopic level. Since then, this new theory has allowed one to<p>explain and describe lots of physical features like the<p>photoelectric effect, the energy levels of atoms, nuclear<p>reactions, It also brought an answer to lots of remaining<p>unanswered questions like the so-called ultraviolet catastrophe.<p>Though, as attractive as this new theory was at that time, some of<p>its counter-intuitive predictions quickly gave rise to<p>controversy. For instance, in 1935, due to one quantum physics<p>feature called entanglement, A. Einstein, B. Podolski and N. Rosen<p>asked the question: "Can quantum-mechanical description of<p>physical reality be considered complete?". This led to<p>the famous debate with N. Bohr and his Copenhagen interpretation.<p>Amongst other particular features of quantum physics one can cite:<p>the superposition principle, the wave function collapse, the<p>Heisenberg uncertainty principle, the wave-particle duality, the<p>no-cloning theorem, As in Alice in wonderland, all those<p>features actually make quantum physics a fascinating world where<p>intuition is most of the time useless.<p><p>In this thesis we tried to observe and study some of the<p>intriguing features of quantum physics. More precisely we tried to<p>use specific light states to explore part of what is called<p>quantum optics.<p><p><p>First we studied the use of coherent states of light to perform<p>tasks you can not perform using classical physics. For instance in<p>1984, Ch. Bennett and G. Brassard proposed the first quantum<p>cryptography protocol which has an absolute security<p>while classical protocol security still relies on some<p>computational assumptions (the assumption is that today<p>computers computational power is not sufficient to threaten the<p>security of classical protocols. Though this means that classical<p>protocols are not intrinsically secure). Since then quantum<p>physics has been proven useful to perform lots of classically<p>impossible tasks like bit commitment, quantum computation, random<p>number generation, In this work we were interested in the<p>problem of coin tossing by telephone introduced by M. Blum<p>in 1981. In this problem two untrustful and distant<p>players try to perform a coin flip. Classically one can show that,<p>if no computational assumptions are made, one of the players can<p>always force the outcome of the coin flip.<p><p>On the opposite if one uses quantum communication resources, a<p>protocol in which none of the players can cheat perfectly can be<p>built, i.e. none of the players have 100\\% chance of<p>winning the protocol even by using the best possible cheating<p>strategy. Moreover this is possible without any other assumption<p>than the validity of the laws of physics. Though a quantum<p>protocol for coin tossing can not completely prevent from cheating, the demonstration of such a protocol would<p>be a proof of principle of the potential of quantum communication<p>to implement classically impossible tasks.<p><p>In our work, we have developed a quantum coin tossing protocol and<p>studied its performances. We have shown that the success cheating<p>probability of the players is bounded by 99,7%<100%, which is<p>better than what is achieved in any classical protocol. One of the<p>originalities of our work is that, for the first time to our<p>knowledge, experimental imperfections (detectors efficiency,<p>losses, limited interference visibility, ) have been taken into<p>account in the theoretical analysis. Moreover, using coherent<p>states of light, we have demonstrated a fiber optic experimental<p>implementation of our protocol and performed a single coin flip<p>where none of the two players could perfectly influence the<p>outcome. This is to our knowledge the first experimental<p>demonstration of single quantum coin tossing.<p><p><p>After coherent states of light, we wanted to work with a more<p>complex quantum state: photon pairs. Not only those states are<p>useful for fundamental physics tests but they also are an<p>important resource for quantum communication. For those reasons<p>our first objective was to build a source that would generate<p>those photon pairs.<p><p>First photon pairs sources were based on bulk nonlinear crystals.<p>Unfortunately the main drawback of those sources is the low<p>collection efficiency of the generated photon pairs. That's why we<p>investigated the possibility of generating the photon pairs<p>directly in a waveguiding structure where they would be readily<p>collected.<p><p>The first solution that we envisaged was to use the natural third<p>order nonlinearity of silica fibers. More precisely the phenomenon<p>we wanted to used is called modulation instability. In this<p>process, two pump photons are destroyed and a photon pair is<p>created with energy and momentum conservations. Moreover we<p>decided to use this process in a photonic crystal fiber. The high<p>confinement of light in this kind of fiber allows a higher<p>nonlinearity and thus a more efficient generation of photon pairs.<p>Finally the fiber we used was birefringent which enables both<p>vectorial and scalar modulation instability to occur.<p><p>As a first experiment, we decided to observe modulation<p>instability in a classical regime where a lot of photons are<p>created. The specific parameters of our photonic crystal fiber -<p>high anomalous dispersion and moderate birefringence - allowed us<p>to observe a regime where the vectorial instability gain band has<p>a similar detuning from the pump as the scalar instability gain<p>band. In this regime we also observed an enhancement of the<p>vectorial gain above the scalar gain which has been confirmed<p>theoretically. To our knowledge this was the first experimental<p>observation of this particular regime of instability.<p><p>To generate photon pairs with this instability process we need to<p>lower down the pump power. Unfortunately we measured that, when<p>pump power was sufficiently lowered to generate ~0,1 photon<p>pairs per pump pulse sent in the fiber, about 75% of generated<p>photons were created by spontaneous Raman scattering and not<p>modulation instability. In order to build an efficient photon pair<p>s secteurs financiers et, en particulier, au rôle de la religion musulmane. Nous montrons que, en moyenne, la finance islamique favorise le développement du secteur bancaire dans les pays musulmans. Plusieurs pays ont en effet réussi à développer un nouveau secteur bancaire compatible avec la Shariah, sans porter ombrage au secteur bancaire non islamique avec lequel il co-existe. Notre analyse empirique est fondée sur une base de données nouvelle et originale. Celle-ci a pour intérêt de fournir des indicateurs de taille et de performance des banques islamiques de dépôt dans le monde, pour la période 2000-2005.<p> Dans le deuxième essai, nous explorons les rendements inconditionnels obtenus sur les marchés boursiers, en particulier les marchés émergents d'actions. Notre analyse d'un large panel de 53 marchés émergents "Majeurs" et "Frontières" confirme les résultats traditionnellement observés dans la littérature. Ainsi, pour l'essentiel, les deux types de marchés sont volatils et émaillés d'événements extrêmes. De plus, les rendements des marchés émergents sont faiblements corrélés avec ceux du reste du monde, même si ces corrélations ont augmenté au cours des derniers décennies. Malgré d'importantes différences en terme de taille et de liquidité, les rendements sur marchés "Frontières" sont qualitativement similaires à ceux des marchés "Majeurs", à l'exception des corrélations. Ces dernières sont en effet actuellement plus faibles dans les marchés "Frontières", qui continuent dès lors à offrir d'importants bénéfices de diversification aux investisseurs internationaux.<p> Dans le dernier essai, nous examinons la relation entre les transferts d'argent des migrants et la croissance économique. Nous confirmons l'idée que les transferts de fonds des migrants sont importants pour les pays en voie de développement. Mais surtout, nous démontrons, de manière théorique et empirique, qu'il est crucial de faciliter dans ces pays l'accès aux comptes de dépôt bancaires, afin de transformer une plus grande part des transferts des migrants en investissements productifs. Ceci est d'autant plus vrai quand l'accès aux autres sources de capitaux internationaux est coûteux.<p>on pairs well defined). A coincidence<p>measurement was performed resulting in a coincidence peak with a<p>7,5 ratio between the peak and the accidental coincidences level.<p>A conversion efficiency $P_s/P_p=1,2,10^{-11}$ was obtained using<p>43 mW of pump power. Moreover photon pairs were generated around<p>1556~nm in the optical communications C-band, which makes them<p>suitable for quantum communication applications using installed<p>fiber optic networks. Finally using the generated photon pairs we<p>performed the Hong-Ou-Mandel experiment highlighting the bosonic<p>nature of photons. We obtained a Mandel dip with a net visibility<p>of 40% in a configuration where the maximum visibility is 50%.<p><p>The photon pair source that we realized is a proof of principle of<p>the high potential of poled fibers in quantum applications. Indeed<p>today, Prof. P. G. Kazansky's team is able to make a 20 cm poled<p>fiber with a nonlinearity $eta_{SH}=8;10^{-2}$\\%/W. If we still<p>suppose 43~mW of pump power, this leads to a $1,0;10^{-9}$<p>conversion efficiency for parametric fluorescence, improving our<p>result by two orders of magnitude. The realization of an efficient<p>photon pair source based on parametric fluorescence in<p>periodically poled twin-hole fiber suitable for quantum<p>applications is thus absolutely possible in a very near future. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

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<p>One of the fundamental predictions of quantum mechanics is the occurrence of random fluctuations which can induce a measurable force between neutral objects, known as the Casimir effect. Casimir effect has attracted a lot of interest in both theoretical and practical work since the first prediction in 1948 because it is the most accessible evidence of quantum electromagnetic fluctuations in vacuum. Besides, it has prospective applications for nanotechnology and for studying fundamental physical theories beyond the standard model. In this dissertation, we report the experimental and theoretical progress towards realizing Casimir-based devices and long sought-after vacuum friction. </p> <p><br></p> <p>First, we propose and experimentally realize the first Casimir diode system that can regulate energy transfer along one direction through quantum vacuum fluctuations. This is the first experimental demonstration of non-reciprocal energy transfer by Casimir effects. We develop a dual-cantilever vacuum system which can be used to measure the Casimir force at separations from 50 nm to 1000 nm.  Parametric coupling scheme is applied to the system to couple two cantilevers with different resonant frequencies by Casimir interaction. By controlling the system near the exceptional point, we are able to break the time reversal symmetry and observe the non-reciprocal energy transfer. </p> <p><br></p> <p>The description of the Casimir diode system is followed by an experimental demonstration of the Casimir transistor system where we achieve the first measurement of Casimir interaction between three macroscopic objects. Three cantilevers can be coupled through quantum vacuum fluctuations by the parametric coupling scheme. Moreover, we have realized the first three-terminal Casimir transistor system that can switch and amplify quantum vacuum mediated energy transfer. These two Casimir-based devices will have potential applications in sensing and information processing.  </p> <p><br></p> <p>Subsequently, the first observation of Casimir mediated non-contact friction is demonstrated experimentally. When two parallel surfaces are moving with a relative velocity, they will experience quantum vacuum friction force which tries to slow down the relative motion because of quantum vacuum fluctuations. The quantum vacuum friction comes from the exchange of virtual photons between two moving bodies.  We have designed a novel method to detect the Casimir force mediated non-contact friction force between two harmonic oscillators. The non-contact friction comes from the interaction of virtual photons and phonons. We have experimentally detected the effect of non-contact friction and successfully measured the friction force at different velocities. </p> <p><br></p> <p>In the latter part of this thesis, two theoretical proposals about detecting the Casimir torque and rotational quantum vacuum friction torque by a levitated optomechanical system are discussed. The optically levitated nanoparticle system is a good candidate for precision measurements because it can achieve an ultrahigh mechanical quality factor due to the well isolation from the thermal environment. The calculation of the Casimir torque on a levitated nanorod near a birefringent plate is demonstrated. The calculation of the rotational quantum vacuum friction torque on a rotating nanosphere near a plate is also presented. By comparing these small torques to the sensitivity of our levitation system, we show that it is feasible to detect the Casimir torque and the rotational quantum vacuum friction torque under realistic conditions in the near future. </p> <p><br></p>