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The Two-Dimensional Bose Gas in Box Potentials Laura Corman

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The Two-Dimensional Bose Gas in Box Potentials Laura Corman The two-dimensional Bose Gas in box potentials Laura Corman To cite this version: Laura Corman. The two-dimensional Bose Gas in box potentials. Physics [physics]. Université Paris sciences et lettres, 2016. English. NNT : 2016PSLEE014. tel-01449982 HAL Id: tel-01449982 https://tel.archives-ouvertes.fr/tel-01449982 Submitted on 30 Jan 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THÈSE DE DOCTORAT de l’Université de recherche Paris Sciences Lettres – PSL Research University préparée à l’École normale supérieure The Two-Dimensional Bose École doctorale n°564 Gas in Box Potentials Spécialité: Physique Soutenue le 02.06.2016 Composition du Jury : par Laura Corman M Tilman Esslinger ETH Zürich Rapporteur Mme Hélène Perrin Université Paris XIII Rapporteur M Zoran Hadzibabic Cambridge University Membre du Jury M Gilles Montambaux Université Paris XI Membre du Jury M Jean Dalibard Collège de France Directeur de thèse M Jérôme Beugnon Université Paris VI Membre invité ABSTRACT Degenerate atomic gases are a versatile tool to study many-body physics. They offer the possibility to explore low-dimension physics, which strongly differs from the three dimensional (3D) case due to the enhanced role of fluctuations. In this work, we study degenerate 2D Bose gases whose original in-plane confi- nement is uniform and of arbitrary shape. These 2D uniform traps, which we first developed on an existing set-up, were subsequently implemented on a new set-up using versatile optical potentials. We present a series of experiments that take advantage of this flexible geo- metry. First, we study the static and dynamic behaviours of a uniform gas at the transition between a 3D normal and a 2D superfluid state. We observe the establishement of extended phase coherence, followed, as the gas is quench cooled, by the apparition of topological defects whose scaling is compared to the Kibble-Zurek prediction. Second, we present the first results of the new set-up : we investigate collective effects in light-matter interactions, where the resonance properties of a dense ensemble of atoms are strongly modified with respect to the single atom ones. Last, we develop two experimental proposals for the new set-up. The first one studies how a 2D gas can be uniformly evaporated using the tilted lattice providing the 2D confinement. In the second one, we propose to produce su- percurrents in a deterministic way in ring-shaped traps either by condensing in an artificial gauge field or by implementing a topological vortex pump. RÉSUMÉ Les gaz quantiques atomiques constituent un outil de choix pour étudier la physique à N corps grâce à leurs nombreux paramètres de contrôle. Ils offrent la possibilité d’explorer la physique en basse dimension, modifiée par rapport au cas à trois dimensions (3D) à cause du rôle accru des fluctuations. Dans ce travail, nous étudions le gaz de Bose à deux dimensions (2D) avec un confine- ment original dans le plan atomique, uniforme et de motif arbitraire. Ces gaz 2D et uniformes, développés sur un montage existant, ont été installés sur un nouveau montage grâce à des potentiels optiques polyvalents. Nous présentons une série d’expériences exploitant cette géométrie flexible. D’abord, nous étudions le comportement statique et dynamique d’un gaz uni- forme lors de la transition d’un état 3D normal vers un état 2D superfluide. Nous observons l’établissement de la cohérence de phase dans un gaz à l’équi- libre puis nous montrons l’apparition après une trempe de défauts topolo- giques dont le nombre est comparé à la prédiction de Kibble-Zurek. Ensuite, nous étudions grâce au nouveau montage les effets collectifs dans l’interaction lumière-matière, où les propriétés de résonance d’un nuage d’atomes dense sont fortement modifiées par rapport à celles d’un atome unique. iii Enfin, nous proposons deux protocoles pour le nouveau montage. Le premier permet d’évaporer de manière uniforme un gaz 2D grâce au réseau incliné du confinement à 2D. Le second propose de produire des supercourants de manière déterministe dans des pièges en anneaux, soit par condensation dans un champ de jauge, soit en réalisant une pompe à vortex topologique. iv REMERCIEMENTS Les performances individuelles, ce n’est pas le plus important. On gagne et on perd en équipe. Zinedine Zidane L’examen du doctorat semble une épreuve solitaire tant pour la rédaction du manuscrit que pour la présentation orale ; ce n’est qu’une apparence, et les résultats présentés ici sont fortement le produit — direct ou indirect — d’une équipe, d’interactions fructueuses avec collègues, amis et famille que j’aimerais remercier ici. Tout d’abord, je tiens à remercier Jean Dalibard qui a accepté que je rejoigne l’expérience rubidium en tant que doctorante. Cela réalisait ainsi une ancienne aspiration de ma part suite à un bref échange que j’avais eu avec lui à la suite d’une conférence de vulgarisation à l’Observatoire de Paris, et qui s’était peu à peu concrétisée grâce à des stages dans son équipe. Ses capacités scientifiques internationalement reconnues sont associées à un souci pédagogique remar- quable qui m’a permis de comprendre énorméments d’aspects de la physique, depuis les cours de l’École polytechnique jusqu’aux discussions impromptues le matin autour d’un tableau et d’un café. Sa modestie et sa bienveillance ont contribué grandement à construire une atmosphère de travail où chacun peut apprendre et proposer ses idées (et je le remercie également d’avoir écouté mes propositions plus ou moins fantaisistes au cours de ces quatre années !). Je tiens également à remercier Jérôme Beugnon qui travaillait sur l’ancienne expérience (dite “rubidium 2”) et qui a pris en main la gestion de l’équipe de la nouvelle expérience “rubidium 3”. Sa franchise, son humour et son pragma- tisme ont permis la construction rapide de l’expérience. La thèse étant rarement un long fleuve tranquille d’un point de vue personnel, je lui suis également très reconnaissante de m’avoir écoutée et aidée lorsque je rencontrais des problèmes pas nécessairement scientifiques qui pouvaient influencer mon travail. Je tiens tout particulièrement à remercier Jean et Jérôme pour leur suivi infail- lible lors du feuilleton des travaux à l’ENS qui ont conduit à l’arrêt prématuré de l’expérience “rubidium 2”, afin de trouver la meilleure solution pour la fin de ma thèse. Rétrospectivement, construire la nouvelle expérience jusqu’à l’obtention de premiers résultats a été un choix très satisfaisant pour moi, et je les remercie à la fois de m’avoir proposé plusieurs options et de m’avoir inté- grée dans la nouvelle équipe. Je remercie également l’école doctorale et Jean- Marc Berroir pour avoir été compréhensifs au vu de la situation des travaux. Mes remerciements vont également à Sylvain Nascimbène, “observateur“ sur les expériences rubidium (en particulier avec le début de la construction de l’expérience dysprosium). Il était toujours possible de passer dans son bureau pour discuter d’un sujet de physique de manière décontractée. Je resterai par- ticulièrement impressionnée par sa capacité de concentration en réunion où v certains points de physique étaient tranchés dans la minute — quand j’espèrai secrètement profiter de quelques minutes de calme en sortant pour réfléchir au problème ! Lors des présentations du métier de chercheur que j’ai eu l’occasion de faire dans des classes de lycée, on n’échappe pas à la traditionnelle “journée-type” du doctorant. Pour moi une certitude : elle a lieu dans la salle de manip, en- tourée de collègues et amis avec qui la discussion permet d’avancer. Je tiens ainsi à remercier toutes les personnes avec lesquelles j’ai travaillé directement au cours de ces quatre années. Tout d’abord, je remercie Rémi pour m’avoir initiée au fonctionnement de l’expérience “rubidium 2”, des boîtiers électron- iques cachés sous la chambre à vide au fonctionnement des mystérieuses switch boxes. Sa capacité à s’attaquer à un problème nouveau pour l’expérience (comme ce fut le cas pour le premier défrichage des possibilités ouvertes par la production de gaz dans des boîtes) a été un exemple pour moi. Je remer- cie également chaleureusement Christof, dont la bonne humeur inattaquable et l’enthousiasme pour les projets m’ont beaucoup aidé lors des moments in- certains de ma première année de thèse. Je garde également un excellent sou- venir de nos convergences musicales, littéraires, etc. Merci également à Lau- riane pour son engagement dans l’expérience, en particulier pour la prise et l’interprétation des données qui ont conduit à la compréhension de la conden- sation transverse. La lente agonie de l’expérience, éprouvée par les marteaux- piqueurs, m’a été moins pénible grâce à Andrea, en stage long, grâce à sa bonne humeur et son autonomie. Je voudrais aussi remercier Tom, avec qui j’ai eu l’occasion de travailler sur les deux expériences. Je garderai en mémoire le comptage de vortex lorsque nous les avons vu apparaître pour la première fois dans les carrés, ainsi que la joie de voir le premier BEC sur “rubidium 3”. Son esprit d’équipe, son dévouement et sa volonté d’en savoir toujours plus ont largement contribué à l’atmosphère très agréable de cette nouvelle expérience.
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