Dissertations / Theses: 'Bose-Einstein condensation'

1

Benson, Eric. "Bose-Einstein condensation of excitons." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0017/NQ48088.pdf.

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2

Arlt, Jan. "Experiments on Bose-Einstein condensation." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326008.

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Davis, Matthew John. "Dynamics of Bose-Einstein condensation." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393350.

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4

Marelic, Jakov. "Bose-Einstein condensation of photons." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/59351.

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A Bose-Einstein condensate can be made of photons. The photons are held at thermodynamic equilibrium in a dye-filled microcavity and pumped with a laser. Thermalisation can be demonstrated and above the threshold a Bose-Einstein condensate will form. A Mach-Zehnder interferometer is built and used to measure the spatial and temporal first-order coherence under various conditions. We build a momentum-resolved spectrometer and use it to obtain views into the phase-space distribution of the photon condensate. We put an upper bound on the value of the interaction strength parameter and find that the microcavity system is ergodic even when not at thermal equilibrium. We build a setup to stabilise the pump laser power with the aim to observe the λ-point of the condensate.

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5

Lewoczko-Adamczyk, Wojciech. "Bose-Einstein condensation in microgravity." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2009. http://dx.doi.org/10.18452/15970.

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Ultra-kalte atomare Gase werden in zahlreichen Laboren weltweit untersucht und finden unter anderem Anwendung in Atomuhren und in Atominterferometer. Die Einsatzgebiete erstrecken sich von der Geodäsie über die Metrologie bis hin zu wichtigen Fragestellungen der Fundamentalphysik, wie z.B. Tests des Äquivalenzprinzips. Doch die beispiellose Messgenauigkeit ist durch die irdische Gravitation eingeschränkt. Zum einen verzerrt die Schwerkraft das Fallenpotential und macht damit die Reduktion der atomaren Energie unter einem bestimmten Limit unmöglich. Zum anderen werden die aus einer Falle frei gelassenen Teilchen durch die Erdanziehung beschleunigt und so ist deren Beobachtungszeit begrenzt. Im Rahmen dieser Arbeit werden die Ergebnisse des Projektes QUANTUS (Quantengase Unter Schwerelosigkeit) dargestellt. Auf dem Weg zur Implementierung eines Quantengasexperimentes im Weltraum wurde innerhalb einer deutschlandweiten Zusammenarbeit eine kompakte, portable und mechanisch stabile Apparatur zur Erzeugung und Untersuchung eines Bose-Einstein-Kondensats (BEC) unter Schwerelosigkeit im Fallturm Bremen entwickelt. Sowohl die Abbremsbeschleunigung von bis zu 50 g als auch das begrenzte Volumen der Fallkapsel stellen hohe Ansprüche an die mechanische Stabilität und die Miniaturisierung von optischen und elektronischen Komponenten. Der Aufbau besteht aus einer im ultra-hoch Vakuum geschlossenen magnetischen Mikrofalle (Atomchip) und einem kompakten auf DFB-Dioden basierenden Lasersystem. Mit diesem Aufbau ließ sich das erste BEC unter Schwerelosigkeit realisieren und nach 1 Sekunde freier Expansion zu beobachten. Weder die schwache Krümmung des Fallenpotentials noch die lange Beobachtungszeit würden in einem erdgebundenen Experiment realisierbar. Die erfolgreiche Umsetzung des Projektes eröffnet ein innovatives Forschungsgebiet - degenerierte Quantengase bei ultratiefen Temperaturen im pK-Bereich, mit großen freien Evolutions- und Beobachtungszeiten von mehreren Sekunden.
Recently, cooling, trapping and manipulation of neutral atoms and ions has become an especially active field of quantum physics. The main motivation for the cooling is to reduce motional effects in high precision measurements including spectroscopy, atomic clocks and matter interferometry. The spectrum of applications of these quantum devices cover a broad area from geodesy, through metrology up to addressing the fundamental questions in physics, as for instance testing the Einstein’s equivalence principle. However, the unprecedented precision of the quantum sensors is limited in terrestial laboratories. Freezing atomic motion can be nowadays put to the limit at which gravity becomes a major perturbation in a system. Gravity can significantly affect and disturb the trapping potential. This limits the use of ultra-shallow traps for low energetic particles. Moreover, free particles are accelerated by gravitational force, which substantially limits the observation time. Targeting the long-term goal of studying cold quantum gases on a space platform, we currently focus on the implementation of a Bose-Einstein condensate (BEC) experiment under microgravity conditions at the drop tower in Bremen. Special challenges in the construction of the experimental setup are posed by a low volume of the drop capsule as well as critical decelerations up to 50g during recapture at the bottom of the tower. All mechanical and electronic components were thus been designed with stringent demands on miniaturization and mechanical stability. This work reports on the observation of a BEC released from an ultra-shallow magnetic potential and freely expanding for one second. Both, the low trapping frequency and long expansion time are not achievable in any earthbound laboratory. This unprecedented time of free evolution leads to new possibilities for the study of BEC-coherence. It can also be applied to enhance the sensitivity of inertial quantum sensors based on ultra-cold matter waves.

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Wu, Biao. "Bose-Einstein condensation of dilute atomic gases." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3037026.

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Ritter, Stephan. "Probing coherence during Bose-Einstein condensation /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17215.

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Ozdemir, Sevilay. "Bose-einstein Condensation At Lower Dimensions." Master's thesis, METU, 2004. http://etd.lib.metu.edu/upload/755959/index.pdf.

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In this thesis, the properties of the Bose-Einstein condensation (BEC) in low dimensions are reviewed. Three dimensional weakly interacting Bose systems are examined by the variational method. The effects of both the attractive and the repulsive interatomic forces are studied. Thomas-Fermi approximation is applied to find the ground state energy and the chemical potential. The occurrence of the BEC in low dimensional systems, is studied for ideal gases confined by both harmonic and power-law potentials. The properties of BEC in highly anisotropic trap are investigated and the conditions for reduced dimensionality are derived.

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9

Mewes, Marc-Oliver. "Bose-Einstein condensation of sodium atoms." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10768.

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10

Fried, Dale G. (Dale George) 1968. "Bose-Einstein condensation of atomic hydrogen." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/84757.

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11

Pereira, Dos Santos Franck. "Condensation de Bose-Einstein de l'hélium métastable." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2002. http://tel.archives-ouvertes.fr/tel-00002267.

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Nous présentons dans ce
mémoire la réalisation expérimentale de la condensation de
Bose-Einstein de l'hélium métastable $2^3S_1$ polarisé. Nous
commençons par y résumer les prédictions théoriques concernant les
taux de collisions élastiques et inélastiques entre atomes
métastables polarisés. Ce sont sur ces prédictions très
encourageantes que reposait l'espoir d'atteindre la condensation
de Bose-Einstein de l'hélium métastable. Nous présentons ensuite
le dispositif expérimental que nous avons construit. La technique
que nous avons utilisée consiste à pré-refroidir un échantillon de
gaz dans un piège magnéto-optique, que l'on charge à partir d'un
jet atomique intense et ralenti. La densité dans le piège
magnéto-optique est limitée par de très forts taux de collisions
inélastiques assistées par la lumière, que nous avons mesurés pour
une large gamme de paramètres de piégeage. Le gaz piégé est
ensuite transféré dans un piège magnétostatique où il est refroidi
par la technique du refroidissement évaporatif jusqu'au seuil de
dégénérescence quantique. Nous avons mesuré des temps de vie des
atomes dans le piège magnétique de l'ordre de la minute, ce qui
démontre que les collisions inélastiques sont supprimées par au
moins deux ordres de grandeur dès lors que les atomes sont
polarisés. A l'aide d'une méthode de détection purement optique,
basée sur l'absorption d'un faisceau laser résonnant à la
traversée du nuage atomique, nous avons pu mettre en évidence la
condensation de Bose-Einstein. Finalement, des mesures du nombre
d'atomes et de la taille du condensat, nous avons déduit une
estimation de la longueur de diffusion, $a=(16\pm8)$ nm.

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12

Shvarchuck, Igor Yevgeniiovich. "Bose-Einstein condensation into non-equilibrium states." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2003. http://dare.uva.nl/document/67440.

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Bedingham, Daniel John. "Quantum field theory and Bose Einstein condensation." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249588.

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Sinclair, Christopher David James. "Bose-Einstein condensation in microtraps on videotape." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428140.

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15

Jones, M. P. A. "Bose Einstein condensation on an atom chip." Thesis, University of Sussex, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270728.

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Pulido, Daniel. "Instability in a cold atom interferometer." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0430103-095432.

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17

Dunningham, Jacob Andrew. "Quantum phase of Bose-Einstein condensates." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:b6cc8b74-753c-4b3e-ad5e-68bd7e32b652.

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The quantum phase of a Bose-Einstein condensate has long been a subject fraught with misunderstanding and confusion. In this thesis we provide a consis- tent description of this phenomenon and, in particular, discuss how phase may be defined, created, manipulated, and controlled. We begin by describing how it is possible to set up a reference condensate against which the phase of other condensates can be compared. This allows us to think of relative phases as if they were absolute and gives a clear and precise definition to 'the phase of a condensate'. A relative phase may also be established by coupling condensates and we show how this can be controlled. We then extend this model to explain how the phase along a chain of coupled condensates can lock naturally without the need for any measurements. The second part of the thesis deals primarily with the link between entangle- ment and phase. We show that, in general, the more entangled a state is, the better its phase resolution. This leads us to consider schemes by which maximally entangled states may be able to be created since these should give the best prac- tical advantages over their classical counterparts. We consider two such states: a number correlated pair of condensates and a Schrodinger cat state. Both schemes are shown to be remarkably robust to loss. A comparison of the merits of these two states, as the inputs to an interferom- eter, reveals very different behaviours. In particular, the number correlated state performs significantly better than the cat state in the presence of loss, which means that it might be useful in interferometry and frequency standard schemes where phase resolution is of the utmost importance. Finally, we propose a scheme for concentrating the entanglement between con- densates, which is an important step in quantum communication protocols. This, along with the ability to manipulate phase and entanglement, suggests that the future for condensates holds not only academic interest but great potential for practical applications.

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18

Moulder, Stuart. "Persistent currents in Bose-Einstein condensates." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648095.

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19

Stickney, James Arthur. "A theoretical analysis of Bose-Einstein condensate based beamsplitters, interferometers, and transistors." Worcester, Mass. : Worcester Polytechnic Institute, 2008. http://www.wpi.edu/Pubs/ETD/Available/etd-032708-124639/.

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20

Grimm, Douglas. "The dynamics of collapsing Bose-Einstein condensates." View electronic text, 2002. http://eprints.anu.edu.au/documents/disk0/00/00/07/64/index.html.

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Thesis (BSc. (Hons))--Australian National University, 2002.
Available via the Australian National University Library Electronic Pre and Post Print Repository. Title from title screen (viewed Mar. 28, 2003). "A thesis submitted for the degree of Bachelor of Science with Honours of The Australian National University" Bibliography: p. 45.

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Petrov, Dmitry Sergeevich. "Bose-Einstein condensation in low-dimensional trapped gases." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2003. http://dare.uva.nl/document/67425.

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22

Fletcher, Richard Jonathan. "Bose-Einstein condensation and superfluidity in two dimensions." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709200.

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23

Harrison, Brent. "Bose-Einstein condensation from a gluon transport equation." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29494.

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In this thesis we investigate the evolution of the quark gluon plasma, as produced in the early stages of a relativistic heavy ion collision, towards equilibrium. To this end we put forward a new numerical scheme to solve the QCD Boltzmann equation in the small-scattering angle approximation, which we develop here for the quenched limit of QCD. We initially restrict our analysis to spatially homogeneous systems of gluons distributed isotropically in momentum space. With our scheme we confirm results of Blaizot et al. [1], in particular that for certain “overpopulated” initial conditions, a transient Bose-Einstein condensate emerges during equilibriation in a finite time. We further analyse the dynamics of the formation of this condensate. We then extend our scheme to systems with cylindrically symmetric momentum distributions, in order to investigate the effects of anisotropy. In particular we compare the rates at which isotropization and equilibriation occur. We also compare our results from the small-scattering angle scheme to the relaxation-time approximation.

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24

Carr, Lincoln D. "Solitons in Bose-Einstein condensates /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9702.

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Palzer, Stefan. "Single impurities in a Bose-Einstein condensate." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609015.

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26

Naik, Devang S. "Bose-Einstein Condensation: Building the Testbeds to Study Superfluidity." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-09072006-141453/.

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Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2007.
Davidovic, Dragomir, Committee Member ; Kennedy, T.A. Brian, Committee Member ; Chapman, Mike, Committee Member ; Raman, Chandra, Committee Chair ; Bunz, Uwe, Committee Member.

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Vorberg, Daniel. "Generalized Bose-Einstein Condensation in Driven-dissipative Quantum Gases." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-234044.

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Bose-Einstein condensation is a collective quantum phenomenon where a macroscopic number of bosons occupies the lowest quantum state. For fixed temperature, bosons condense above a critical particle density. This phenomenon is a consequence of the Bose-Einstein distribution which dictates that excited states can host only a finite number of particles so that all remaining particles must form a condensate in the ground state. This reasoning applies to thermal equilibrium. We investigate the fate of Bose condensation in nonisolated systems of noninteracting Bose gases driven far away from equilibrium. An example of such a driven-dissipative scenario is a Floquet system coupled to a heat bath. In these time-periodically driven systems, the particles are distributed among the Floquet states, which are the solutions of the Schrödinger equation that are time periodic up to a phase factor. The absence of the definition of a ground state in Floquet systems raises the question, whether Bose condensation survives far from equilibrium. We show that Bose condensation generalizes to an unambiguous selection of multiple states each acquiring a large occupation proportional to the total particle number. In contrast, the occupation numbers of nonselected states are bounded from above. We observe this phenomenon not only in various Floquet systems, i.a. time-periodically-driven quartic oscillators and tight-binding chains, but also in systems coupled to two baths where the population of one bath is inverted. In many cases, the occupation numbers of the selected states are macroscopic such that a fragmented condensation is formed according to the Penrose-Onsager criterion. We propose to control the heat conductivity through a chain by switching between a single and several selected states. Furthermore, the number of selected states is always odd except for fine-tuning. We provide a criterion, whether a single state (e.g., Bose condensation) or several states are selected. In open systems, which exchange also particles with their environment, the nonequilibrium steady state is determined by the interplay between the particle-number-conserving intermode kinetics and particle-number-changing pumping and loss processes. For a large class of model systems, we find the following generic sequence when increasing the pumping: For small pumping, no state is selected. The first threshold, where the stimulated emission from the gain medium exceeds the loss in a state, is equivalent to the classical lasing threshold. Due to the competition between gain, loss and intermode kinetics, further transitions may occur. At each transition, a single state becomes either selected or deselected. Counterintuitively, at sufficiently strong pumping, the set of selected states is independent of the details of the gain and loss. Instead, it is solely determined by the intermode kinetics like in closed systems. This implies equilibrium condensation when the intermode kinetics is caused by a thermal environment. These findings agree well with observations of exciton-polariton gases in microcavities. In a collaboration with experimentalists, we observe and explain the pump-power-driven mode switching in a bimodal quantum-dot micropillar cavity
Die Bose-Einstein-Kondensation ist ein Quantenphänomen, bei dem eine makroskopische Zahl von Bosonen den tiefsten Quantenzustand besetzt. Die Teilchen kondensieren, wenn bei konstanter Temperatur die Teilchendichte einen kritischen Wert übersteigt. Da die Besetzungen von angeregten Zuständen nach der Bose-Einstein-Statistik begrenzt sind, bilden alle verbleibenden Teilchen ein Kondensat im Grundzustand. Diese Argumentation ist im thermischen Gleichgewicht gültig. In dieser Arbeit untersuchen wir, ob die Bose-Einstein-Kondensation in nicht wechselwirkenden Gasen fern des Gleichgewichtes überlebt. Diese Frage stellt sich beispielsweise in Floquet-Systemen, welche Energie mit einer thermischen Umgebung austauschen. In diesen zeitperiodisch getriebenen Systemen verteilen sich die Teilchen auf Floquet-Zustände, die bis auf einen Phasenfaktor zeitperiodischen Lösungen der Schrödinger-Gleichung. Die fehlende Definition eines Grundzustandes wirft die Frage nach der Existenz eines Bose-Kondensates auf. Wir finden eine Generalisierung der Bose-Kondensation in Form einer Selektion mehrerer Zustände. Die Besetzung in jedem selektierten Zustand ist proportional zur Gesamtteilchenzahl, während die Besetzung aller übrigen Zustände begrenzt bleibt. Wir beobachten diesen Effekt nicht nur in Floquet-Systemen, z.B. getriebenen quartischen Fallen, sondern auch in Systemen die an zwei Wärmebäder gekoppelt sind, wobei die Besetzung des einen invertiert ist. In vielen Fällen ist die Teilchenzahl in den selektierten Zuständen makroskopisch, sodass nach dem Penrose-Onsager Kriterium ein fragmentiertes Kondensat vorliegt. Die Wärmeleitfähigkeit des Systems kann durch den Wechsel zwischen einem und mehreren selektierten Zuständen kontrolliert werden. Die Anzahl der selektierten Zustände ist stets ungerade, außer im Falle von Feintuning. Wir beschreiben ein Kriterium, welches bestimmt, ob es nur einen selektierten Zustand (z.B. Bose-Kondensation) oder viele selektierte Zustände gibt. In offenen Systemen, die auch Teilchen mit der Umgebung austauschen, ist der stationäre Nichtgleichgewichtszustand durch ein Wechselspiel zwischen der (Teilchenzahl-erhaltenden) Intermodenkinetik und den (Teilchenzahl-ändernden) Pump- und Verlustprozessen bestimmt. Für eine Vielzahl an Modellsystemen zeigen wir folgendes typisches Verhalten mit steigender Pumpleistung: Zunächst ist kein Zustand selektiert. Die erste Schwelle tritt auf, wenn der Gewinn den Verlust in einer Mode ausgleicht und entspricht der klassischen Laserschwelle. Bei stärkerem Pumpen treten weitere Übergänge auf, an denen je ein einzelner Zustand entweder selektiert oder deselektiert wird. Schließlich ist die Selektion überraschenderweise unabhängig von der Charakteristik des Pumpens und der Verlustprozesse. Die Selektion ist vielmehr ausschließlich durch die Intermodenkinetik bestimmt und entspricht damit den oben beschriebenen geschlossenen Systemen. Ist die Kinetik durch ein thermisches Bad hervorgerufen, tritt wie im Gleichgewicht eine Grundzustands-Kondensation auf. Unsere Theorie ist in Übereinstimmung mit experimentellen Beobachtungen von Exziton-Polariton-Gasen in Mikrokavitäten. In einer Kooperation mit experimentellen Gruppen konnten wir den Modenwechsel in einem bimodalen Quantenpunkt-Mikrolaser erklären

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Rogel-Salazar, Jesus. "Aspects of Bose-Einstein condensation and Bessel beam resonators." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397329.

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Sheard, Benjamin T. "Magnetic transport and Bose-Einstein condensation of rubidium atoms." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:dedece2b-c33a-415b-9d6b-570263042797.

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This thesis describes the design, construction and optimisation of a new apparatus to produce Bose-Einstein condensates (BECs) of 87Rb atoms. The main aim in building this system was to include a high resolution imaging system capable of resolving single atoms. Optical access for the imaging system was created by including a stage of atom transport in which the atoms are magnetically transferred ~50 cm from a magneto-optical trap (MOT), where they are initially collected, to a glass science cell where experiments are carried out and imaging takes place. Two magnetic transport schemes have been demonstrated, based on approaches first used in other laboratories. First, a scheme in which the atoms are transferred in a moving pair of magnetic trapping coils. Second, a hybrid scheme where the atoms are translated part of the distance in the moving coils, and the rest of the way by switching the current in a chain of fixed coils. This second scheme was designed to allow optical access for a high numerical aperture microscope objective to be placed immediately next to the science cell for high resolution imaging. The atoms were first collected in a large pyramid MOT which can be loaded with 3 × 10^9 atoms in a time of 20 s. Around half of these atoms – those in the |F = 1, mF = −1> magnetic substate – were then magnetically trapped prior to transport. The typical fraction of the trapped atoms transferred to the science cell was ~30% and ~18% for the moving coils and hybrid schemes respectively. Evaporative cooling was carried out on the atom cloud following transport with the moving coils and loading into a time-orbiting potential trap. The optimised cooling sequence lasted for 28 s and consistently produced a pure condensate with 5 × 10^5 atoms. A BEC has also been produced by evaporative cooling following hybrid transport. The next experimental steps will be to optimise the hybrid transfer approach further and install the high resolution imaging system. The system is well-placed to continue an ongoing series of experiments in which ultracold atoms are trapped in RF-dressed potentials. These potentials will be used to study low-dimensional quantum gases as well as in experiments where small atom number BECs are rapidly rotated to enter the fractional quantum Hall regime.

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Benedicto, Orenes Daniel. "Realization of a spin-1 Bose-Einstein condensation experiment." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8073/.

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This thesis is devoted to the construction, optimization and characterization of an experimental apparatus, capable of creating spinor condensates of ~1x10^5 atoms with a repetition rate of 10s, using an all-optical evaporation technique. I report a complete description of the experimental apparatus and techniques used in the experiment and a characterization of the BEC sample. We study the transmission of absorption imaging pictures through a coherent fiber bundle. We show that the fiber bundle introduces spurious noise in the picture mainly due to the strong core-to-core coupling. We demonstrate that we can retrieve exact quantitative information about the atomic system using this technique. We also explore the equilibration dynamics of ferromagnetic spin-1 system as a function of the initial magnetization of the sample and the external magnetic field. We show that the magnetization of the system is conserved despite of the presence of dissipative processes that are intrinsic to any experiment. We investigated the formation of the BEC in a spin-1 quantum gas in the presence of an external magnetic field. We report on the spontaneous magnetization of the condensate fraction during the evaporation process at low magnetic fields. We as well observe multi-step condensation, and found signatures of a possible interspecies Feshbach resonance.

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Yu, Yichao. "Realization of Bose-Einstein condensation with Lithium-7 atoms." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92672.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 49).
This thesis presents our work on developing and improving the techniques of trapping and cooling an ultra-cold cloud of Lithium-7 atoms and the realization of the Bose- Einstein condensate as a first step to study quantum magnetism in optical lattice. The techniques used in this experiment include Zeeman slowing, magneto-optical trapping (MOT), gray molasses, static magnetic trapping, evaporative cooling, optical dipole trapping (ODT), etc. The apparatus has the capability of creating a Bose-Einstein condensate with almost 106 atoms in 10 seconds as well as tuning the interaction between atoms in a BEC using the Feshbach resonance with a magnetic bias field of up to ~~ 1000G.
by Yichao Yu.
S.B.

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32

Scharnberg, Falk. "Bose-Einstein condensation in micro-potentials for atom interferometry." Swinburne Research Bank, 2007. http://hdl.handle.net/1959.3/22734.

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Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, 2007.
Submitted in fulfilment of requirements for the degree of Doctor of Philosophy, [Faculty of Engineering and Industrial Sciences], Swinburne University of Technology, 2007. Typescript. Bibliography: p. [207]-224.

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Michelangeli, Alessandro. "Bose-Einstein condensation: Analysis of problems and rigorous results." Doctoral thesis, SISSA, 2007. http://hdl.handle.net/20.500.11767/4185.

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This work is an up-to-date and partially improved analysis of the basics of the mathe- matical description of Bose-Einstein condensation in terms of first principles of Quantum Mechanics. The main aims are: 1) to provide a compact, yet coherent overview: - of the basic mathematical tools used to formalise Bose-Einstein condensation, - of the mathematical techniques for studying several features of this physical phenomenon, - and of how such means emerge as the natural ones in connection with their physical interpretation; 2) to discuss and to place in the above perspective some new contributions and improvements: - on equivalent characterizations of Bose-Einstein condensation, - on the strength of the convergence for some currently available asymptotic results, - and on the effects of interparticle correlations on the energy and the dynamics of the many-body condensate.

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Norrie, Adam Anson, and n/a. "A classical field treatment of colliding Bose-Einstein condensates." University of Otago. Department of Physics, 2005. http://adt.otago.ac.nz./public/adt-NZDU20061025.121803.

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In this thesis we develop a fully quantum-mechanical treatment of collisions between distinct atomic Bose-Einstein condensate wavepackets, with particular emphasis on the incoherently scattered atoms that form s-wave haloes around the condensate wavepackets. Previous theoretical treatments of these systems have been unable to account simultaneously for both the evolution of the halo and the depletion of the condensates, and were therefore restricted to the small scattering limit. Our approach uses the truncated Wigner method, a particular example of the classical field methods familiar from quantum optics. The atomic field is restricted to a low-energy subspace of single-particle states, and the method is applicable even to highly-scattered systems. We present a comprehensive derivation of the truncated Wigner method for ultracold bosonic fields, and discuss in detail the validity regime of the Wigner truncation for inhomogeneous multimode systems. The method gives rise to a set of coupled stochastic differential equations that describe the evolution of a single realisation of the atomic field, and have a form similar to that of the well known Gross-Pitaevskii equation, but with the important difference that the stochastic differential equations include well prescribed quantum fluctuations. To propagate our systems we develop algorithms that allow for highly efficient numerical evolution of realistic experimental collisions. By investigating individual trajectories of the colliding system, we find that the scattering halo is composed of many distinct highly-populated phase grains separated by large numbers of vortices, a behaviour we label quantum turbulence. We develop a spatial averaging method for approximately calculating quantum correlation functions from a single trajectory, and calculate various properties of the halo. Based on these results, we propose a mechanism to explain the observed features of scattering halo formation. We find by using an appropriately extended truncated Wigner approach that three-body recombination events have negligible effect on the collisions. Using an ensemble of trajectories we calculate correlation functions of a particular collisional system to give a rigorous characterisation of the quantum statistics of the field, and obtain results that are remarkably similar to those obtained using single trajectory spatial averaging. For global field quantities, such as the total coherent population, we find that accurate estimates can be achieved using just two trajectories, a result we use to efficiently explore the dependence of the system on key physical parameters. Finally, we apply the truncated Wigner method to collisions between condensates in differing hyperfine states, whose (single-trajectory and ensemble) behaviour we find is qualitatively similar to that of single-component collisions.

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35

Wynar, Roahn Helden. "Ultra-cold molecules in an atomic Bose-Einstein condensate /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004403.

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36

Salmond, Grant Leonard. "Nonlinear dynamics of Bose-Einstein condensates : semiclassical and quantum /." St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16406.pdf.

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37

Schmidutz, Tobias Fabian. "Studies of a homogeneous Bose gas." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708544.

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38

Zhang, Mei. "Entanglement and spin squeezing of bose condensed atoms." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/27675.

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39

Gotlibovych, Igor. "Degenerate Bose gases in a uniform potential." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708187.

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40

Oliveira, Felipe Dimer de. "Efeitos de Densidade nos Processos de Fotoassociação em Condensados de Bose-Einstein." Universidade Federal Fluminense, 2004. http://www.bdtd.ndc.uff.br/tde_busca/arquivo.php?codArquivo=422.

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Conselho Nacional de Desenvolvimento Cientifico e Tecnológico
Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro
Nesta tese abordaremos os processos de fotoassociação em condensação de Bose- Einstein. Estes podem ser resumidos da seguinte forma: um condensado formados por átomos, inicialmente no estado fundamental, é iluminado com laseres de freqüência adequada, de tal modo que os átomos se combinem em moléculas. Tudo isto sem que o condensado deixe de existir por conta de instabilidades envolvidas neste processo. O que acabamos de descrever tem um equivalente na ótica quântica: a geração de segundo harmônico, cujas equações são semelhantes as do condensado. A natureza mais complexa das interações entre átomos, bem como a consideração de graus de liberdade internos, inclui efeitos potencialmente mais interessante que os encontrados com a luz. A quantidade de fenômenos que pode ser abordada é muito grande. As ressonâncias de Feshbach, por exemplo, são capazes de alterar a natureza da interação interatômica. Também podemos ter dois átomos fermiônicos formando uma molécula bosónica. Há efeitos de interferência entre dois condensados e estudos teóricos concernentes a fase relativa entre eles. Também é importante citarmos os estudo sobre vórtices e momento angular, enfim, há todo um zoológico de idéias a serem propostas teoricamente ou experimentalmente. Assim como em 1911 repentinamente surgiram novas áreas de estudo devido a descoberta da supercondutividade, aqui ocorre algo semelhante, uma fronteira da física foi aberta e devemos explora-la até que novos limites sejam alcançados.

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41

Jackson, Brian. "Vortices in trapped Bose-Einstein condensates." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4241/.

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In this thesis we solve the Gross-Pitaevskii equation numerically in order to model the response of trapped Bose-Einstein condensed gases to perturbations by electromagnetic fields. First, we simulate output coupling of pulses from the condensate and compare our results to experiments. The excitation and separation of eigen-modes on flow through a constriction is also studied. We then move on to the main theme of this thesis: the important subject of quantised vortices in Bose condensates, and the relation between Bose-Einstein condensation and superfluidity. We propose methods of producing vortex pairs and rings by controlled motion of objects. Full three-dimensional simulations under realistic experimental conditions are performed in order to test the validity of these ideas. We link vortex formation to drag forces on the object, which in turn is connected with energy transfer to the condensate. We therefore argue that vortex formation by moving objects is intimately related to the onset of dissipation in superfluids. We discuss this idea in the context of a recent experiment, using simulations to provide evidence of vortex formation in the experimental scenario. Superfluidity is also manifest in the property of persistent currents, which is linked to vortex stability and dynamics. We simulate vortex line and ring motion, and find in both cases precessional motion and thermodynamic instability to dissipation. Strictly speaking, the Gross-Pitaevskii equation is valid only for temperatures far below the BEG transition. We end the thesis by describing a simple finite- temperature model to describe mean-field coupling between condensed and non- condensed components of the gas. We show that our hybrid Monte-Carlo/FFT technique can describe damping of the lowest energy excitations of the system. Extensions to this model and future research directions are discussed in the conclusion.

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42

Yi, Su. "Properties of trapped dipolar condensates." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/27356.

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43

Boţan, Vitalie. "Bose-Einstein Condensation of Magnetic Excitons in Semiconductor Quantum Wells." Doctoral thesis, Uppsala University, Department of Physics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7112.

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In this thesis regimes of quantum degeneracy of electrons and holes in semiconductor quantum wells in a strong magnetic field are studied theoretically. The coherent pairing of electrons and holes results in the formation of Bose-Einstein condensate of magnetic excitons in a single-particle state with wave vector K. We show that correlation effects due to coherent excitations drastically change the properties of excitonic gas, making possible the formation of a novel metastable state of dielectric liquid phase with positive compressibility consisting of condensed magnetoexcitons with finite momentum. On the other hand, virtual transitions to excited Landau levels cause a repulsive interaction between excitons with zero momentum, and the ground state of the system in this case is a Bose condensed gas of weakly repulsive excitons. We introduce explicitly the damping rate of the exciton level and show that three different phases can be realized in a single quantum well depending on the exciton density: excitonic dielectric liquid surrounded by weakly interacting gas of condensed excitons versus metallic electron-hole liquid. In the double quantum well system the phase transition from the excitonic dielectric liquid phase to the crystalline state of electrons and holes is predicted with the increase of the interwell separation and damping rate.

We used a framework of Green's function to investigate the collective elementary excitations of the system in the presence of Bose-Einstein condensate, introducing "anomalous" two-particle Green's functions and symmetry breaking terms into the Hamiltonian. The analytical solution of secular equation was obtained in the Hartree-Fock approximation and energy spectra were calculated. The Coulomb interactions in the system results in a multiple-branch structure of the collective excitations energy spectrum. Systematic classification of the branches is proposed, and the condition of the stability of the condensed excitonic phase is discussed.

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44

Roux, Cédric. "Condensation de Bose-Einstein sur une puce à atomes supraconductrice." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00300440.

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Dans les expériences de puces à atomes, des gaz froids d'atomes alcalins peuvent être maintenus dans un piège magnétique à une distance de quelques microns d'une surface conductrice. La présence de la surface peut se révéler gênante pour le piégeage. En effet, les fluctuations du champ magnétique induites par le bruit de courant dans la puce engendrent des pertes et diminuent le temps de vie de l'échantillon dans le piège quand le nuage se rapproche de la surface. Ce bruit magnétique de champ proche est dû à la résistivité du conducteur métallique utilisé pour le piégeage. L'une des solutions à ce problème pourrait être l'utilisation de supraconducteurs.

Cette thèse présente la première expérience de puce à atomes supraconductrice. Nous avons en particulier obtenu le premier condensat de Bose-Einstein au voisinage d'un fil de niobium. Le condensat est composé d'environ 10.000 atomes à une température de 100 nK, à 50 micromètres de la surface de la puce. Les résultats obtenus au cours de ce travail montrent donc la faisabilité de la condensation de Bose-Einstein à quelques dizaines de microns d'une surface supraconductrice.

Nous avons également calculé l'effet sur les atomes piégés du bruit de champ proche créé par la dynamique du réseau de vortex dans le supraconducteur. La dissipation dans les zones normales n'est pas négligeable, mais le temps de vie calculé reste très au-dessus des temps de vie mesurés au voisinage de conducteurs normaux. Ces prévisions théoriques confèrent aux puces à atomes supraconductrices un réel potentiel en termes d'applications des micropièges magnétiques très confinants. Ainsi, nous prévoyons par exemple de coupler le nuage atomique à des dispositifs supraconducteurs quantiques mésoscopiques, comme des cavités linéaires ou des SQUIDs.

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45

Du, Shengwang. "Atom-chip Bose-Einstein condensation in a portable vacuum cell." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3165812.

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46

Boţan, Vitalie. "Bose-Einstein condensation of magnetic excitons in semiconductor quantum wells /." Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7112.

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47

Yoon, Min Sung. "Experiments on magnetic transport, magnetic trapping and Bose-Einstein condensation." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497161.

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48

Ueda, Hiroaki. "Study on various phases emerging from magnon Bose-Einstein condensation." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120630.

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49

Bismut, Gabriel. "Excitations d’un condensat de Bose-Einstein dipolaire." Paris 13, 2012. http://scbd-sto.univ-paris13.fr/intranet/edgalilee_th_2012_bismut.pdf.

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Nos expériences ont été consacrées à l’étude d’un condensat de chrome, élément possédant un fort moment magnétique. Elles nous ont permis de mettre en évidence l’inﬂuence des interactions dipolaires sur les propriétés hydrodynamiques et magnétiques d’un condensat. Ces interactions sont, contrairement aux interactions de contact, anisotropes et à longue portée. Nous avons étudié un mode d’oscillations collectives, de type quadrupolaire, du condensat de chrome. Nous avons observé que la fréquence de ce mode dépend légèrement de l’orientation des dipôles, ﬁxée par le champ magnétique. De plus, nous avons utilisé la diﬀusion de Bragg pour sonder le spectre des excitations de Bogoliubov du condensat. Nous avons caractérisé l’eﬀet des interactions dipolaires sur les énergies d’excitation. Dans le régime phononique, nous en avons déduit une anisotropie de la vitesse du son, qui dépend de la direction de propagation de l’onde sonore relativement à l’axe de polarisation des dipôles. Nous avons également étudié les collisions inélastiques dues à l’interaction dipôle-dipôle, appelées relaxations dipolaires. Nous avons observé, d’une part, que le taux de collision est directement lié aux corrélations de paires dans le condensat, et d’autre part, que ce taux dépend fortement de la dimensionnalité du système. À très bas champ magnétique, nous avons mis en évidence une dynamique spinorielle, due aux interactions dipolaires, qui se traduit par une démagnétisation spontanée du condensat. Ces expériences ont été facilitées par la mise au point d’une cavité optique passive “ultra-stable”, utilisée pour asservir nos nouveaux lasers
Abstract : In our experiments, we have studied a chromium Bose-Einstein condensate. Because of the strong magnetic moment of chromium, these experiments enabled us to characterize the inﬂuence of dipolar interactions on the hydrodynamic and magnetic properties of a condensate. These interactions are anisotropic and long range, as opposed to contact interactions. We have studied a “quadrupole-like” collective excitation mode of the chromium condensate. We have observed that the frequency of this mode is dependent on the orientations of the atomic dipoles, given by the direction of the external magnetic ﬁeld. Moreover, we have used Bragg spectroscopy in order to measure the shift caused by dipolar interactions on the Bogoliubov excitations energies. In the phononic regime, our results reveal the anisotropy of the velocity of sound, which depends on the direction of the sound wave with respect to the axis of the dipoles. We have also studied dipolar relaxation, which is a type of inelastic collision caused by dipolar interactions. We have observed that the collision rate is directly related to pair correlations in the condensate. Furthermore, we have shown that this rate is strongly dependent on the dimensionality of the system. At very low magnetic ﬁelds, dipolar interactions are responsible for a spontaneous demagnetization of the condensate, which we have also observed. Our experiments were made easier by the building of a passive optical cavity, which was used to eﬀectively stabilize our new lasers

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50

Geursen, Reece Wim, and n/a. "Experiments with Bose-Einstein condensates in optical potentials." University of Otago. Department of Physics, 2005. http://adt.otago.ac.nz./public/adt-NZDU20070131.162251.

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We present a detailed experimental investigation into Bose-Einstein condensates loaded into a one-dimensional optical standing wave at the Bragg condition. The main emphasis of this thesis is the experimental and theoretical investigation into Bragg spectroscopy performed on circularly accelerating Bose-Einstein condensates. The condensate undergoes circular micromotion in a magnetic time-averaged orbiting potential trap and the effect of this motion on the Bragg spectrum is analysed. A simple frequency modulation model is used to interpret the observed complex structure, and broadening effects are considered using numerical solutions to the Gross-Pitaevskii equation. The second part of this thesis is an experimental investigation into the effect of nonlinearity on the non-adiabatic loading of a condensate into a optical lattice at the Brillouin zone boundary. Results of using a phase shifting technique to load a single Bloch band in the presence of strong interactions are presented. We observe a depletion of the condensed component, and we propose possible mechanisms for this result.

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Dissertations / Theses on the topic 'Bose-Einstein condensation'

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