Die Nutzung von Quanteneigenschaften für die Informationsverarbeitung, die sogenannte Quanteninformationsverarbeitung (QIP), ist ein seit zwei Jahrzehnten zunehmend populäres Forschungsfeld. Es hat sich gezeigt, dass Einzelphotonen die am besten geeigneten Träger für den Transport von Quanteninformation über weite Strecken sind. Obwohl viele Methoden zur Erzeugung von Einzelphotonen existieren, wurde bisher nur wenig Forschungsarbeit an schmalbandigen Einzelphotonen, d.h. mit spektralen Breiten im MHz-Bereich geleistet. Allerdings sind solche Einzelphotonen besonders wichtig, wenn Kopplungen zwischen Einzelphotonen und atomaren Systemen, die oft als Verarbeitungseinheiten in der QIP genutzt werden, realisiert werden sollen. Diese Doktorarbeit befasst sich mit mehreren Forschungsaspekten zu schmalbandigen Einzelphotonen, die von Bedeutung sind, wenn solche Photonen als Informationsträger genutzt werden sollen. Zunächst wird eine Quelle von schmalbandigen Einzelphotonen vorgestellt, die auf dem Konzept der parametrischen Fluoreszenz innerhalb eines optischen Resonators basiert und die einen konstanten Strom von Photonenpaaren emittiert. Eine statistische Beschreibung dieser Photonenpaare wird vorgestellt und erstmals direkt gemessen. Um Emission in nur eine einzelne Mode zu erreichen, wurde der Photonenstrom mit Hilfe eines speziell entwickelten Mehrpass-Fabry-Perot-Etalons mit geringem Durchlassbereich und sehr hohem Kontrast gefiltert. Photon-Atom-Wechselwirkungen werden im zweiten Teil der Arbeit gezeigt. Der Effekt der elektromagnetisch induzierten Transparenz (EIT) wird vorgestellt und experimentell demonstriert. Die ersten EIT Experimente in Cäsiumgaszellen bei Raumtemperatur mit Probepulsen, die nur ein einzelnes Photon enthalten, werden demonstriert. Schließlich zeigt ein umfassender Ausblick wie die entwickelten experimentellen Bausteine erweitert werden können, um Einzelphotonenspeicherung zu erlauben und die Technologie für Quantenrepeater zu demonstrieren. / The use of quantum mechanical properties for information processing, so-called quantum information processing (QIP) has become an increasingly popular research field in the last two decades. It turned out that single photons are the most reliable long distance carriers of quantum information, e.g., tools to connect different processing nodes in QIP. While several methods exist to produce single photons, only little research has been performed so far on narrow-band single photons with spectral bandwidths in the MHz regime. Such photons are, however, of particular importance when coupling of single photons to atomic systems, which are often used in QIP as processing nodes, shall be realized. This thesis covers several research aspects on narrow-band single photons, all of which are important if such photons should be used as quantum information carriers. At first, a source for narrow-band single photons is introduced. This source is based on the concept of parametric down-conversion inside an optical resonator. It emits a constant stream of photon pairs. One of the two photons from the pair can be detected heralding the presence of the other photon. A statistical description of these photon pairs is introduced and for the first time also directly measured. In order to reach single-mode single-photon emission, the stream of photons was filtered with a specifically developed multi-pass Fabry-Perot etalon. This filter has a passband FWHM of only 165 MHz and particularly high contrast.

Une mémoire quantique réversible permettant de stocker et relire de l'information quantique est une composante majeure dans la mise en œuvre de nombreux protocoles d'information quantique. Comme la lumière est un porteur de l'information quantique fiable sur des longues distances, et comme les atomes offrent la possibilité d'obtenir de longues durées de stockage, le recherche actuelle sur la création d'une mémoire quantique se concentre sur la transfert des fluctuations quantiques de la lumière sur des cohérences atomiques. Le travail réalisé durant cette thèse porte sur le développement d'une mémoire quantique pour la lumière comprimée, utilisant un ensemble d'atomes froids de Césium stock'es dans un piege magnéto-optique. Nos deux principaux objectifs étaient le développement d'une source de lumière non-classique, et le développement d'un milieu atomique pour le stockage de celle-ci. Tout d'abord, nous commençons par présenter la construction d'un oscillateur paramétrique optique qui utilise un cristal non-linéaire de PPKTP. Cet OPO fonctionne comme source d'états de vide comprime résonant avec la raie D2 du Césium. Nous caractérisons ces états grâce à une reconstruction par tomographie quantique, en utilisant une approche de vraisemblance maximale. Ensuite, nous examinons une nouvelle expérience qui nous permet d'utiliser comme milieu de stockage des atomes froids de Césium dans un piège magneto-optique récemment développé. Car cette expérience exige l'utilisation de nouveaux outils et techniques, nous discutons le développement de ceux-ci, et comment ils ont contribue à notre progression vers le stockage des états quantiques dans nos atomes des Césium, et finalement vers l'intrication de deux ensembles atomiques.

Made available in DSpace on 2016-06-02T20:16:52Z (GMT). No. of bitstreams: 1 5357.pdf: 11039751 bytes, checksum: 1534d2a0d9db4a8e8f0feb6c57f55080 (MD5) Previous issue date: 2013-08-01 / Financiadora de Estudos e Projetos / The simultaneously incidence of two light beams on one or more atoms causes destructive interference of these beams in atomic states causing cancellation of the absorption of one of the incident beams and this phenomenon is called Electromagnetically Induced Transparency (EIT). The main objective of this work is to show that the Electromagnetically Induced Transparency, which is usually studied in the quantum context, can be modeled classically as a function of coupled harmonic oscillators subject to an external force and dissipation. To will establish the classical equivalence, it will be presented the theory of the EIT in diferent quantum systems and also the theory of classic harmonic oscillators. Analogies will be performed comparing the classical and quantum equations of motion obtained for each scheme. For this, we perform the equivalence of EIT in quantum systems as atoms in three levels in Λ configuration, two-level atoms plus a cavity mode and the cavity optomechanics with the classical system of two coupled harmonics oscillator forced and damped. We also analyze the equivalence of two diferent quantum systems: three level atoms plus one cavity mode and four levels atoms in free space with a classical system composed by three coupled harmonic oscilators, forced and damped, in diferent configurations. / A incidência simultânea de dois feixes luminosos em um ou mais átomos provoca a interferência destrutiva desses feixes em um dos estados atômicos causando o cancelamento da absorção de um dos feixes incidentes e esse fenômeno é denominado Transparência Eletromagneticamente Induzida (\Electromagnetically Induced Transparency", EIT). O objetivo principal deste trabalho é mostrar que a Transparência Eletromagneticamente Induzida, que é normalmente estudada no contexto quântico, pode ser modelada classicamente em função de osciladores harmônicos amortecidos forçados e acoplados. Para que a equivalência clássica seja bem fundamentada, será apresentada a teoria da EIT em diversos sistemas quânticos e também a teoria dos osciladores harmônicos clássicos. As equivalências serão realizadas comparando as equações de movimento clássicas e quânticas obtidas para cada regime. Para isso, vamos realizar a equivalência da EIT em sistemas quânticos de átomos de três níveis em configuração Λ, dois níveis atômicos mais um modo da cavidade e a optomecânica de cavidades com o sistema clássico de dois osciladores harmônicos amortecidos forçados e acoplados. Logo após, será analisada a equivalência de dois sistemas quânticos compostos por átomos de três níveis mais um modo da cavidade e átomos de quatro níveis com os sistemas clássicos de três osciladores harmônicos amortecidos forçados e acoplados em diferentes configurações.

Orientador: Luís Eduardo Evangelista de Araujo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T04:46:52Z (GMT). No. of bitstreams: 1 BecerraCastro_EmilioManuel_D.pdf: 3066640 bytes, checksum: 3e7ff0e58dae7364f9f6d0b5f37924eb (MD5) Previous issue date: 2012 / Resumo: Neste tese apresentamos um estudo teórico dos efeitos de coerência atómica em vapor atómico com o propósito de estudar teoricamente efeitos óticos não-lineares transversais a baixas intensidades de luz. Sob a condição da transparência induzida eletromagneticamente, um meio atómico pode desenvolver não-linearidades óticas gigantes, possibilitando a observação de efeitos óticos não-lineares a baixas intensidades. Investigamos três efeitos transversais: emissão cónica, focalização induzida e feixes de vórtices induzidos eletromagneticamente. Todos estes três efeitos têm origem na modulação de fase cruzada entre um laser de prova e um laser sinal, ambos fracos, com intensidades abaixo da intensidade de saturação das transições às quais estão acopladas. Em emissão cónica, descrevemos a formação de anéis ao redor de um feixe de prova fraco. No estudo de focalização induzida, descrevemos como que a aplicação de uma máscara de intensidade ao feixe sinal pode levar à formação de lentes GRIN no vapor atómico, induzindo à focalização do laser de prova. Por último, estudamos a conversão do feixe de prova em um feixe de vórtice ótico pela aplicação de uma máscara de intensidade espiral ao feixe sinal / Abstract: In this thesis we present theoretical study of the effects of atomic coherence in atomic vapor for the purpose of studying theoretically transverse nonlinear optical effects at low light levels. Under the conditions of electromagnetically induced transparency, an atomic medium can develop giant optical nonlinearities, allowing the observation of nonlinear optical effects to low intensities. We investigate three transverse effects: conical emission, induced focusing and electromagnetically induced vortices. All three of these effects stem from cross-phase modulation between probe and a signal laser, both weak with intensities below the saturation intensity the transitions to they coupled. In conical emission, we describe the formation of rings around a weak probe beam. In the study of induced focusing, we describe how applying an intensity mask to the signal beam can lead to the formation of GRIN lenses the atomic vapor, leading to focusing of the probe laser. Finally, we studied the conversion of the probe beam into an optical vortex beam by applying a spiral intensity mask to the signal beam / Doutorado / Física / Doutor em Ciências

Nous étudions expérimentalement deux mémoires quantiques pour la lumière utilisant la transparence électromagnétiquement induite (EIT) dans des nuages froids de césium.Nous expliquons la pertinence des mémoires quantiques pour le développement de réseaux quantiques à longue distance, et décrivons la théorie de l’EIT en soulignant les paramètres essentiels pour l’implémentation de mémoires quantiques.Notre premier cas d’étude est un piège magnéto-optique en espace libre. Notre principal résultat est la démonstration du caractère multimode de ce système pour le stockage quantique de la lumière. Pour cela, nous utilisons des faisceaux de Laguerre-Gauss (LG), porteurs de moment angulaire orbital (OAM). Dans une première étape, nous avons montré que l’état de moment orbital d’impulsions lumineuses en régime de photons uniques est préservé lors du stockage dans la mémoire. Ensuite, nous avons implémenté un bit quantique comme une superposition de modes LG ayant des hélicités opposées. Nous avons développé un système original pour mesurer ces bits quantiques qui nous a permis de caractériser l’action de la mémoire. Nous avons ainsi pu montrer que le stockage quantique de ces bits quantiques.Le second système, également un nuage d’atomes froids, a la particularité que les atomes sont piégés optiquement autour d’un nano-guide d’onde. Ce design innovant permet une plus grande interaction entre lumière et matière, et facilite l’interfaçage des photons dans et hors de la mémoire. Nous décrivons la construction de ce dispositif et les premiers pas vers son utilisation en tant que mémoire quantique. / We present an experimental study of two optical quantum memory systems based on electromagnetically induced transparency (EIT) in cold cesium atoms.We explain the relevance of quantum memories for the development of large-scale quantum networks, we give a comprehensive theory of the EIT phenomenon and underline the role of relevant parameters regarding the implementation of quantum memories.The first system under study is prepared in a free-space magneto-optical trap. The main result of this thesis is the demonstration of the spatial multimode capability of this system at the quantum level. For this, we used Laguerre-Gaussian (LG) light beams, i.e. beams possessing a non-zero value of orbital angular momentum (OAM). In a first step, we showed that the orbital angular momentum of stored light pulses is preserved by the memory, deep in the single photon regime. In a second step, we encoded information in the orbital angular momentum state of a weak light pulse and defined a qubit using two LG beams of opposite helicities. We developed an original setup for the measurement of this OAM qubit and used it to characterize the action of the memory during the storage of such a light pulse. Our results show that the memory performs the quantum storage of such a qubit.The second system under study, also a cloud of cold atoms, has the specificity that the atoms are trapped optically in the vicinity of a nano-waveguide. This innovative design ensures a higher light-matter interaction and facilitates the interfacing of photons into and out of the memory. We describe the building of this setup and the first steps towards quantum memory implementations.

The author presents the successful development of an on-chip, monolithic, integrated rubidium vapor-cell. These vapor-cells integrate ridge waveguide techniques with hollow-core waveguiding technology known as Anti-Resonant Reflecting Optical Waveguides (ARROWs). These devices are manufactured on-site in BYU's Integrated Microelectronic Laboratory (IML) using common silicon wafer microfabrication techniques. The ARROW platform fabrication is outlined, but the bulk of the dissertation focuses on novel packaging techniques that allow for the successful introduction and sealing of rubidium vapor into these micro-sized vapor-cells. The unique geometries and materials utilized in the ARROW platform render common vapor-cell sealing techniques unusable. The development of three generations of successful vapor-cells is chronicled. The sealing techniques represented in these three generations of vapor-cells include high-temperature epoxy seals, cold-weld copper crimping, variable pressure vacuum capabilities, indium solder seals, and electroplated passivation coatings. The performance of these seals are quantified using accelerated lifetime tests combined with optical spectroscopy. Finally, the successful probing of the rubidium absorption spectrum, electromagnetically induced transparency, and slow light on the ARROW-based vapor-cell platform is reported.

No description available.

In this Master’s thesis, we have focused on the description of three-level quantum systems through master equations for their density matrix, involving a recently proposed non-linear thermodynamic one. The first part is focused on a three-level system interacting with two heat baths, a hot and a cold one. We investigated the rate of heat flow from the hot to the cold bath through the quantum system, and how the steady-state is approached. Additional calculations here refer to the rate of entropy production and the evolution of all elements of the density matrix of the system from an arbitrary initial state to their equilibrium or steady-state value. The results are compared against those of a linear, Lindblad-type master equation designed so that for a quantum system interacting with only one heat bath, the same final Gibbs steady state is attained. In the second part of this thesis, we focus on the electromagnetically induced transparency (EIT), a phenomenon typically achievable only in atoms with specific energy structures. For a three level system (to which the present study has focused), for example, EIT requires two dipole allowed transitions (the 1-3 and the 2-3) and one forbidden (the 1-2). The phenomenon is observed when a strong laser (termed the control laser) is tuned to the resonant frequency of the upper two levels. Then, as a weak probe laser is scanned in frequency across the other transition, the medium is observed to exhibit both: a) transparency at what was the maximal absorption in the absence of the coupling field, and b) large dispersion effects at the atomic resonance. We discuss the Hamiltonian describing the phenomenon and we present results from two types of master equations: a) an empirically modified Von-Neumann one allowing for decays from each energy state, and b) a typical Lindblad one, with time-dependent operators. In the first case, an analytical solution is possible, which has been confirmed through a direct solution of the full master equation. In the second case, only numerical results can be obtained. We present and compare results from the two master equations for the susceptibility of the system with respect to the probe field, and we discuss them in light also of available experimental data for this very important phenomenon. / Η παρούσα εργασία επικεντρώνεται στην περιγραφή των κβαντικών συστημάτων τριών καταστάσεων μέσω εξισώσεων master για την μήτρα πυκνότητας πιθανότητάς τους (density matrix), συμπεριλαμβάνοντας μία πρόσφατα προτεινόμενη μη-γραμμική θερμοδυναμική εξίσωση. Το πρώτο μέρος εστιάζει σε ένα σύστημα τριών καταστάσεων το οποίο βρίσκεται σε αλληλεπίδραση με δύο λουτρά θερμότητας, ένα θερμό και ένα ψυχρό. Εξετάζεται ο ρυθμός ροής θερμότητας από το θερμό προς το ψυχρό λουτρό μέσω του κβαντικού συστήματος, και με ποιον τρόπο επιτυγχάνεται η μόνιμη κατάσταση. Επιπλέον υπολογισμοί αναφέρονται στον ρυθμό παραγωγής της εντροπίας και στην εξέλιξη όλων των στοιχείων της μήτρας πυκνότητας πιθανότητας από μία τυχαία αρχική κατάσταση προς την ισορροπία ή τη μόνιμη κατάσταση. Τα αποτελέσματα παρουσιάζονται συγκριτικά με εκείνα μιας γραμμικής, τύπου Lindblad master εξίσωσης, κατάλληλα σχεδιασμένης ώστε στην ειδική περίπτωση ενός κβαντικού συστήματος σε αλληλεπίδραση με ένα λουτρό θερμότητας επιτυγχάνεται η ίδια τελική μόνιμη κατάσταση Gibbs. Στο δεύτερο μέρος, εστιάζουμε στην ηλεκτρομαγνητικά επαγόμενη διαφάνεια (electromagnetically induced transparency (EIT)), ένα φαινόμενο το οποίο τυπικά είναι εφικτό μόνο σε άτομα με ειδικές ενεργειακές δομές. Για ένα σύστημα τριών καταστάσεων (στο οποίο επικεντρώνεται η παρούσα εργασία), για παράδειγμα, το ΕΙΤ απαιτεί δύο διπολικά επιτρεπτές μεταβάσεις (την 1-3 και την 2-3) και μία απαγορευμένη (την 1-2). Το φαινόμενο παρατηρείται όταν ένα ισχυρό laser (το αποκαλούμενο ως control laser) συντονίζεται στη συχνότητα των δύο άνω ενεργειακών σταθμών. Τότε, καθώς ένα ασθενές probe laser ανιχνεύεται με συχνότητα όμοια με της άλλης επιτρεπόμενης μετάβασης, το μέσο παρατηρείται να εμφανίζει τα εξής: α) διαφάνεια στο σημείο μέγιστης απορρόφησης απουσία του control πεδίου, και β) έντονα φαινόμενα διασποράς στον ατομικό συντονισμό. Θα συζητήσουμε τη Χαμιλτονιανή που περιγράφει το φαινόμενο και θα παρουσιάσουμε αποτελέσματα από δύο εξισώσεις master: α) μία εμπειρική τροποποιημένη Von-Neumann εξίσωση επιτρέποντας τις απώλειες από κάθε ενεργειακή κατάσταση, και β) μία τυπική Lindblad εξίσωση, με χρόνο-εξαρτώμενους τελεστές. Στην πρώτη περίπτωση, είναι πιθανή η εύρεση μιας αναλυτικής λύσης, η οποία έχει επιβεβαιωθεί μέσω μιας άμεσης (direct) λύσης της πλήρους εξίσωσης master. Στη δεύτερη περίπτωση, μπορούν να ληφθούν μόνο αριθμητικά αποτελέσματα. Παρουσιάζονται και συγκρίνονται τα αποτελέσματα που ελήφθησαν από τις δύο master εξισώσεις και αφορούν την επιδεκτικότητα (susceptibility) του συστήματος σε σχέση με το probe πεδίο, και τέλος συζητιούνται σε σχέση με διαθέσιμα πειραματικά δεδομένα γι’ αυτό το πολύ σημαντικό φαινόμενο.

Στην εργασία αυτή μελετούμε φαινόμενα μεταβατικής (χρονικά εξαρτημένης) απορρόφησης σε δύο συστήματα κβαντικών τελειών, κάτω από συνθήκες που οδηγούν τις κβαντικές τελείες να εμφανίσουν σε στάσιμη κατάσταση φαινόμενα οπτικής διαφάνειας, και πιο συγκεκριμένα ηλεκτρομαγνητικά επαγόμενη διαφάνεια και οπτική διαφάνεια λόγω εξωτερικού δυναμικού. Μετά από μια σχετικά σύντομη εισαγωγή στις κβαντικές τελείες και στο φαινόμενο και την ιστορία της ηλεκτρομαγνητικά επαγόμενης διαφάνειας, τα συστήματα των κβαντικών τελειών μελετώνται με την μεθοδολογία του πίνακα πυκνότητας, η οποία αναπτύσσεται στην παρούσα εργασία. Τα αποτελέσματα που εξάγουμε προκύπτουν από αριθμητικές λύσεις των αντίστοιχων εξισώσεων του πίνακα πυκνότητας για διάφορες τιμές παραμέτρων. / In this thesis we study transient absorption in two quantum dot systems under the conditions of optical transparency. We will study two types of transparency; the first is voltage-controlled transparency and the second electromagnetically induced transparency. The thesis starts with a short introduction in quantum dot nanostructures that is followed by an introduction to the phenomenon and the history of electromagnetically induced transparency. We then study the coherent interaction of the electromagnetic fields with the quantum dots with the methodology of the density matrix that is analysed in the thesis. We solve the appropriate density matrix equations numerically for the structures under study and present results for several system parameters.

The author of this thesis concentrates his attention on quantum optical properties of some artificial electromagnetic media, such as quantum coherent atomic vapors (various multilevel electromagnetically induced transparency vapors) and negative refractive index materials, and suggests some possible ways to manipulate wave propagations inside the artificial electromagnetic materials based on quantum coherence and quantum vacuum effects. In Chapters 1 and 2, the author reviews the previous papers on quantum coherence as well as the relevant work such as electromagnetically induced transparency (EIT), atomic population trapping and their various applications. The basic concepts of quantum coherence (atomic phase coherence, quantum interferences within atomic energy levels) and quantum vacuum are introduced, and the theoretical formulations for treating wave propagations in quantum coherent media are presented. In Chapter 3, the author considers three topics on the manipulation of light propagations via quantum coherence and quantum interferences: i) the evolutional optical behaviors (turn-on dynamics) of a four-level N-configuration atomic system is studied and the tunable optical behavior that depends on the intensity ratio of the signal field to the control field is considered. Some typical photonic logic gates (e.g. NOT and NOR gates) are designed based on the tunable four-level optical responses of the N-configuration atomic system; ii) the destructive and constructive quantum interferences between two control transitions (driven by the control fields) in a tripod-type four-level system is suggested. The double-control quantum interferences can be utilized to realize some photonic devices such as the logic-gate devices, e.g., NOT, OR, NOR and EXNOR gates; iii) some new quantum coherent schemes (using EIT and dressed-state mixed-parity transitions) for realizing negative refractive indices are proposed. The most remarkable characteristic (and advantage) of the present scenarios is such that the isotropic left-handed media (with microscopic structure units at the atomic level) in the optical frequency band can be achieved. Quantum vacuum (the ground state of quantized fields) can exhibit many interesting effects. In Chapter 4, we investigate two quantum-vacuum effects in artificial materials: i) the anisotropic distribution of quantum-vacuum momentum density in a moving electromagnetic medium; ii) the angular momentum transfer between quantum vacuum and anisotropic medium. Such quantum-vacuum macroscopic mechanical effects could be detected by current technology, e.g., the so-called fiber optical sensor that can measure motion with nanoscale sensitivity. We expect that these vacuum effects could be utilized to develop sensitive sensor techniques or to design new quantum optical and photonic devices.In Chapter 5, the author suggests some interesting effects due to the combination of quantum coherence and quantum vacuum, i.e., the quantum coherent effects, in which the quantum-vacuum fluctuation field is involved. Two topics are addressed: i) spontaneous emission inhibition due to quantum interference in a three-level system; ii) quantum light-induced guiding potentials for coherent manipulation of atomic matter waves (containing multilevel atoms). These quantum guiding potentials could be utilized to cool and trap atoms, and may be used for the development of new techniques of atom fibers and atom chips, where the coherent manipulation of atomic matter waves is needed.In Chapter 6, we conclude this thesis with some remarks, briefly discuss new work that deserves further consideration in the future, and present a guide to the previously published papers by us. / QC 20100810