Émission quantique spontanée : modifications induites par l’environnement

The control of the spontaneous emission of quantum emitters is of fundamental importance for the development of future quantum technologies, like quantum cryptography or quantum computing. Such applications rely on the manipulation of atoms, molecules, or "artificial" atoms, as elementary sources of light, and on the exploitation of the quantum nature of the emitted light, single photons. With the recent developments in nanofabrication techniques and nanotechnologies, the modification of the dynamics of the spontaneous emission by the environment is being investigated at the level of a few emitters, allowing for unprecedented control and manipulation of the spontaneous emission. In parallel to the experimental efforts, theoretical understanding of the fundamental interaction mechanisms between quantum emitters and their environment also becomes more and more essential.In this thesis, we tackle three different paradigms of the spontaneous emission phenomenon, all dealing with modifications of the spontaneous emission induced the environment. Firstly, we tackle the problem of monitored spontaneous emission, that is how the processus of emission is modified when the emitting system is being frequently monitored by an external observer, and which is closely related to the problem of measurementin quantum mechanics. Secondly, we consider the interaction between quantum emitters and optical resonances supported by nearby nanostructures. Finally, we study the remote interaction between quantum emitters and surfaces engraved with nanostructures which are designed and arranged in specific patterns, so-called metasurfaces.We present and deal with different formalisms to model such different situations, interfacing different fields of physics like quantum optics and nanophotonics. In each of these situations, we illustrate with realistic theoretical predictions how the spontaneous emission is modified: in the first case, how the lifetime of the quantum emitter is altered,in the second case how the frequency of the emitted photon is altered, and in the last situation how the environment may induce quantum coherence in the emitter. For each case, for provide with experimental proposals for future confirmations of these predictions, to bring a better understanding and control over these fundamental processes.Le contrôle de l’émission spontanée d’émetteurs quantiques est d’une importance capitale dans le développement des futures technologies quantiques telles que la cryptographie ou l’ordinateur quantiques. La base de ces applications consiste en la manipulation d’atomes, de molécules ou d’atomes « artificiels » comme sources élémentaires de lumière, et en l’exploitation de la nature quantique de la lumière émise, constituée de photonsuniques. Grâce au développement récent des techniques de nanofabrication et des nanotechnologies, la modification de l’émission spontanée par l’environnement est en train d’être explorée au niveau de quelques émetteurs seulement, ce qui ouvre la voie vers un contrôle et une manipulation de l’émission spontanée sans précédent. En parallèle des efforts expérimentaux, une compréhension théorique des mécanismes d’interactionfondamentaux entre émetteurs quantiques et leur environnement devient également indispensable.Dans cette thèse, nous considérons l’émission spontanée dans trois paradigmes différents traitant de la modification de ce processus due à l’environnement. Dans le premier, nous considèrons le problème du « monitorage » de l’émission spontanée, c’est-à-dire le fait qu’un observateur extérieur puisse modifier le processus d’émission par des mesures fréquentes de l’état du système, ce qui est étroitement relié au problème de la mesure en mécanique quantique. Dans un deuxième temps, nous considérons l’interaction d’émetteurs quantiques avec des résonances optiques supportées par des structures nanométriques placées à proximité. Enfin, nous traitons de l’interaction lointaine entre des émetteurs et des surfaces gravées avec des nanostructures fabriquées et positionnéesselon un motif particulier, appelées métasurfaces. Nous présentons et utilisons plusieurs formalismes pour modéliser ces différentes situations, qui interfacent divers domaines de la physique comme l’optique quantique et la nanophotonique. Nous illustrons chaque situation par des prédictions théoriques réalistes sur la manière dont l’émission spontanée est modifiée : dans le premier cas, par une altération de la durée de vie de l’émetteur, dans le second, par une altération de la fréquence du photon qui est émis, et, dans la dernière situation, comment l’environnement peut induire à longue distance une cohérence quantique chez l’émetteur. Pour chacune de ces prédictions, nous faisons des propositions expérimentales pour de futures confirmations de ces effets, afin d’améliorer notre compréhension et le contrôle de ces processus fondamentaux d’interaction lumière-matière

Joint Anaphoricity Detection and Coreference Resolution with Constrained Latent Structures

International audienceThis paper introduces a new structured model for learninganaphoricity detection and coreference resolution in a jointfashion. Specifically, we use a latent tree to represent the fullcoreference and anaphoric structure of a document at a globallevel, and we jointly learn the parameters of the two modelsusing a version of the structured perceptron algorithm.Our joint structured model is further refined by the use ofpairwise constraints which help the model to capture accuratelycertain patterns of coreference. Our experiments on theCoNLL-2012 English datasets show large improvements inboth coreference resolution and anaphoricity detection, comparedto various competing architectures. Our best coreferencesystem obtains a CoNLL score of 81:97 on gold mentions,which is to date the best score reported on this setting

Apprentissage d'une hiérarchie de modèles à paires spécialisés pour la résolution de la coréférence

National audienceNous proposons une nouvelle méthode pour améliorer significativement la performance des modèles à paires de mentions pour la résolution de la coréférence. Étant donné un ensemble d'indicateurs, notre méthode apprend à séparer au mieux des types de paires de mentions en classes d'équivalence, chacune de celles-ci donnant lieu à un modèle de classification spécifique. La procédure algorithmique proposée trouve le meilleur espace de traits (créé à partir de combinaisons de traits élémentaires et d'indicateurs) pour discriminer les paires de mentions coréférentielles. Bien que notre approche explore un très vaste ensemble d'espaces de trait, elle reste efficace en exploitant la structure des hiérarchies construites à partir des indicateurs. Nos expériences sur les données anglaises de la CoNLL-2012 Shared Task indiquent que notre méthode donne des gains de performance par rapport au modèle initial utilisant seulement les traits élémentaires, et ce, quelque soit la méthode de formation des chaînes ou la métrique d'évaluation choisie. Notre meilleur système obtient une moyenne de 67.2 en F1-mesure MUC, B3 et CEAF ce qui, malgré sa simplicité, le situe parmi les meilleurs systèmes testés sur ces données

Conditions for anti-Zeno effect observation in free-space atomic radiative decay

Frequent measurements can modify the decay of an unstable quantum state with respect to the free dynamics given by Fermi's golden rule. In a landmark article, Nature 405, 546 (2000), Kofman and Kurizki concluded that in quantum decay processes, acceleration of the decay by frequent measurements, called the quantum anti-Zeno effect (AZE), appears to be ubiquitous, while its counterpart, the quantum Zeno effect, is unattainable. However, up to now there have been no experimental observations of the AZE for atomic radiative decay (spontaneous emission) in free space. In this work, making use of analytical results available for hydrogen-like atoms, we find that in free space, only non-electric-dipolar transitions should present an observable AZE, revealing that this effect is consequently much less ubiquitous than first predicted. We then propose an experimental scheme for AZE observation, involving the electric quadrupole transition between D 5/2 and S 1/2 in the heaviest alkali-earth ions Ca + and Sr +. The proposed protocol is based on the STIRAP technique which acts like a dephasing quasi-measurement

Structured learning with latent trees: a joint approach to coreference resolution

This thesis explores ways to define automated coreference resolution systems by using structured machine learning techniques. We design supervised models that learn to build coreference clusters from raw text: our main objective is to get model able to process documentsglobally, in a structured fashion, to ensure coherent outputs. Our models are trained and evaluated on the English part of the CoNLL-2012 Shared Task annotated corpus with standard metrics. We carry out detailed comparisons of different settings so as to refine our models anddesign a complete end-to-end coreference resolver. Specifically, we first carry out a preliminary work on improving the way features areemployed by linear models for classification: we extend existing work on separating different types of mention pairs to define more accurate classifiers of coreference links. We then define various structured models based on latent trees to learn to build clusters globally, andnot only from the predictions of a mention pair classifier. We study different latent representations (various shapes and sparsity) and show empirically that the best suited structure is some restricted class of trees related to the best-first rule for selecting coreference links. Wefurther improve this latent representation by integrating anaphoricity modelling jointly with coreference, designing a global (structured at the document level) and joint model outperforming existing models on gold mentions evaluation. We finally design a complete end-to-endresolver and evaluate the improvement obtained by our new models on detected mentions, a more realistic setting for coreference resolution

Interplay between spontaneous decay rates and Lamb shifts in open photonic systems

International audienceIn this letter, we describe the modified decay rate and photonic Lamb (frequency) shift of quantum emitters in terms of the resonant states of a neighboring photonic resonator. This description illustrates a fundamental distinction in the behaviors of closed (conservative) and open (dissipative) systems: the Lamb shift is bounded by the emission linewidth in closed systems while it overcomes this limit in open systems

Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields

The Gemini Multi-conjugate adaptive optics System (GeMS) is a facility instrument for the Gemini-South telescope. It delivers uniform, near-diffraction-limited image quality at near-infrared wavelengths over a 2 arcminute field of view. Together with the Gemini South Adaptive Optics Imager (GSAOI), a near-infrared wide field camera, GeMS/GSAOI's combination of high spatial resolution and a large field of view will make it a premier facility for precision astrometry. Potential astrometric science cases cover a broad range of topics including exo-planets, star formation, stellar evolution, star clusters, nearby galaxies, black holes and neutron stars, and the Galactic center. In this paper, we assess the astrometric performance and limitations of GeMS/GSAOI. In particular, we analyze deep, mono-epoch images, multi-epoch data and distortion calibration. We find that for single-epoch, un-dithered data, an astrometric error below 0.2 mas can be achieved for exposure times exceeding one minute, provided enough stars are available to remove high-order distortions. We show however that such performance is not reproducible for multi-epoch observations, and an additional systematic error of ~0.4 mas is evidenced. This systematic multi-epoch error is the dominant error term in the GeMS/GSAOI astrometric error budget, and it is thought to be due to time-variable distortion induced by gravity flexure.Comment: 16 pages, 22 figures, accepted for publication in MNRA

Improving pairwise coreference models through feature space hierarchy learning

International audienceThis paper proposes a new method for significantly improving the performance of pairwise coreference models. Given a set of indicators, our method learns how to best separate types of mention pairs into equivalence classes for which we construct distinct classification models. In effect, our approach finds an optimal feature space (derived from a base feature set and indicator set) for discriminating coreferential mention pairs. Although our approach explores a very large space of possible feature spaces, it remains tractable by exploiting the structure of the hierarchies built from the indicators. Our experiments on the CoNLL-2012 Shared Task English datasets (gold mentions) indicate that our method is robust relative to different clustering strategies and evaluation metrics, showing large and consistent improvements over a single pairwise model using the same base features. Our best system obtains a competitive 67:2 of average F1 over MUC, B3 , and CEAF which, despite its simplicity, places it above the mean score of other systems on these datasets

Joint Anaphoricity Detection and Coreference Resolution with Constrained Latent Structures

International audienceThis paper introduces a new structured model for learninganaphoricity detection and coreference resolution in a jointfashion. Specifically, we use a latent tree to represent the fullcoreference and anaphoric structure of a document at a globallevel, and we jointly learn the parameters of the two modelsusing a version of the structured perceptron algorithm.Our joint structured model is further refined by the use ofpairwise constraints which help the model to capture accuratelycertain patterns of coreference. Our experiments on theCoNLL-2012 English datasets show large improvements inboth coreference resolution and anaphoricity detection, comparedto various competing architectures. Our best coreferencesystem obtains a CoNLL score of 81:97 on gold mentions,which is to date the best score reported on this setting

Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements

Dielectric nanostructures have demonstrated optical antenna effects due to Mie resonances. Preliminary investigations on dielectric nanoantennas have been carried out for a trifecta of enhancements, i.e., simultaneous enhancements in absorption, emission directionality and radiative decay rates of quantum emitters. However, these investigations are limited by fragile substrates or low Purcell factor, which is extremely important for exciting quantum emitters electrically. In this paper, we present a Si mix antenna array to achieve the trifecta enhancement of ~1200 fold with a Purcell factor of ~47. The antenna design incorporates ~10 nm gaps within which fluorescent molecules strongly absorb the pump laser energy through a resonant mode. In the emission process, the antenna array increases the radiative decay rates of the fluorescence molecules via Purcell effect and provides directional emission through a separate mode. This work could lead to novel CMOS compatible platforms for enhancing fluorescence for biological and chemical applications.Comment: 20 pages, 4 figure