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Ultracold Atom-Ion Systems in Hybrid TrapsOkeyo, Onyango Stephen 21 November 2017 (has links)
Diese Arbeit beschäftigt sich mit der theoretischen Beschreibung eines Hybridsystems eines ultrakalten neutralen Atoms und eines einzelnen Ions. Diese Hybrid-Atom-Ion-Systeme verbinden die wichtigsten Vorteile von ultrakalten neutralen Atomen und Ionen. Neutrale Atome sind leicht skalierbar vor allem und können in großen Stückzahlen vorbereitet werden, wahrend gefangene Ionen über längere Zeiten gelagert werden können und leicht kontrollierbar sind. Einige der vorgeschlagenen Aussichten der hybriden Quantensysteme umfassen die sympathische Kühlung von eingefangenen Ionen, die ultrakalte Chemie, das Quantum Informationsverarbeitung, und Atom-Ionen-Quantensimulatoren. Diese Anwendungen erfordern eine äußerst präzise Steuerung und damit eine sehr genaue theoretische Modellierung. Eine neue Methode, die eine vollständige sechsdimensionale Behandlung von zwei Partikeln ermöglicht In räumlich getrennten dreidimensionalen Fangpotentialen wurde entwickelt. Indem man die raumliche Verschiebung zwischen den Einfangpotentialen erlaubt, ist es möglich, die gesteuerte Bewegung eines einzelnen Ions durch ein optisches Gitterpotential zu beschreiben, das mit neutralen Atomen gefüllt ist. Die Wechselwirkung zwischen dem neutralen Atom und dem geladenen Ion wird durch eine realistische Born-Oppenheimer Potentialkurve beschrieben. Eines der hier diskutierten Hybridsysteme ist 7Li2+ Isotop, das mit der neu entwickelten Methode untersucht wird, dabei wurden vermiedene Kreuzungen im Energiespektrum zwischen molekularen Zuständen und den Schwingungszuständen des Fallenpotentials als Funktion des Abstandes zwischen den beide Fallen beobachtet. Diese vermiedenen Kreuzungen bestatigen die bereits vorhergesagten falleninduzierten Resonanzen, die mithilfe der Quantendefekttheorie bestimmt wurden. Ebenfalls werden die erst kürzlich entdeckten inelastischen falleninduzierten Resonanzen in ultrakalten Atomen auch in den Atom-Ion Systemen beobachtet. / This thesis deals with the theoretical description of a hybrid system of an ultracold neutral atom and a single ion. These hybrid atom-ion systems combine the key advantages of ultracold neutral atoms and ions. In particular, neutral atoms are easily scalable and can be prepared in large numbers, while trapped ions can be stored for much longer times and are easy to control. Some of the proposed prospects of the hybrid quantum systems include sympathetic cooling of trapped ions, ultracold chemistry, quantum information processing, and atom-ion quantum simulators. These applications require extremely precise control and thus very accurate theoretical modeling. A new method that allows for a full 6-dimensional treatment of two particles in spatially separated 3-dimensional trapping potentials was developed. By allowing for the spatial displacement between the trapping potentials, it is possible to describe the controlled motion of a single ion through an optical-lattice potential filled with neutral atoms. The interaction between the neutral atom and the ion is modeled using realistic Born-Oppenheimer potential curves from ab initio quantum chemistry calculations. An application of the developed approach to the hybrid atom-ion system reveals avoided crossings between the molecular bound states and the unbound trap states as a function of the separation between the two traps. These avoided crossings correspond to trap-induced resonances. This finding confirms the trap-induced resonances predicted earlier based on quantum-defect-theory calculations. Also, the recently found inelastic confinement-induced resonances in ultracold neutral atoms are demonstrated to be present in atom-ion systems. These resonances arise due to the coupling between the center-of-mass and relative motions. The inelastic confinement-induced resonances could be used in coherent molecular ion formation and in the determination of atom-ion scattering properties like the scattering lengths.
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Colisões Inelásticas Frias em Amostras Heteronucleares obtidas em Armadilhas Magneto-Ópticas. / Cold inelastic collisions in two species magneto optical traps.Telles, Gustavo Deczka 30 September 1998 (has links)
Um estudo das taxas de perda de átomos ocorrendo numa armadilha magneto-óptica mista foi realizado aqui. Observamos experimentalmente, pela primeira vez, a ocorrência de processos colisionais inelásticos envolvendo duas espécies atômicas distintas. Identificamos o escape radiativo como o processo dominante nas taxas de perda de átomos da armadilha de sódio, devidas às colisões desses com os átomos de rubídio aprisionados, para as dadas condições experimentais. Realizamos estudos semelhantes com uma mistura K-Rb, onde as taxas de perda de átomos da armadilha de potássio foram observadas. Procurou-se interpretar os resultados através um modelo semiclássico que teve de ser modificado por nós. Esses estudos foram importantes porque revelaram a grande influência do processo de escape radiativo nas taxas de perda. Também verificou-se que outros canais podem manifestar a sua influência e suspeitamos que isso se deva às diferenças estruturais das \"quasimoléculas\" formadas na colisão. A compreensão de processos colisionais em armadilhas magneto-ópticas mistas é importante para a obtenção e estudo de amostras distintas de condensados bosônicos coexistindo numa mesma região. / We report the results of the trap-Ioss collisional rates observed in a mixed species magneto-optical trapo These are the first systematic studies about the collisionalloss channels due to heteronuclear interactions between two cold atomic sampIes in aMOr. We have used two different combinations: Na-Rb and K -Rb. lt was observed that the rates are strongly affected by the radiative escape Ioss channel, especially in the Na-Rb system. We also observed that some other Ioss channels may ruIe the rates behavior depending on the combination or the experimento To understand the results a semiclassical approach was used: the Gallagher-Prichard theory. We beIieve that these studies will soon be helpful to control the interatomic collisional rates for the achievement of heteronuclear sampIes of Bose-Einstein condensates.
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Estudo de colisões entre átomos de Rydberg ultrafrios em amostras atômicas aprisionadas numa armadilha óptica de dipolo / Study of collisions between ultracold Rydberg atoms in atomic samples trapped in an optical dipole trapKondo, Jorge Douglas Massayuki 18 December 2014 (has links)
Neste trabalho, estudamos colisões entre átomos de Rydberg ultrafrios em uma amostra atômica de alta densidade aprisionada em uma armadilha óptica de dipolo (AOD) tipo QUEST (Quasi Electrostatic Trap). Nossos objetivos incluíam testar a manifestação de fenômenos de muitos corpos bem como estudar efeitos de anisotropia nos processos colisionais envolvendo dois corpos. Para isso, escolhemos o processo colisional descrito por 5/2+5/2(+2)3/2+(2)7/2 no intervalo de 37 ≤ ≤47. O processo foi estudado na ausência e presença de campo elétrico estático, originando as ressonâncias Förster. Os resultados mostram que mesmo em alta densidade atômica o processo de dois corpos domina a interação, apesar da clara manifestação do bloqueio dipolar. Após modificações na montagem experimental, estudamos um dos picos da ressonância Förster 375/2+375/2393/2+357/2 em função da direção e amplitude em relação ao eixo longitudinal da AOD. Discutimos os resultados e os desafios futuros do experimento. / In this paper, we study collisions between ultracold Rydberg atoms in a high density atomic sample trapped in an optical dipole trap (ODT), type QUEST (Quasi Electrostatic Trap). Our goals included testing the manifestation of many-body phenomena and to study anisotropy effects in collisional processes involving two Rydberg atoms. In order to do this, we have chosen the collision process described by 5/2+5/2(+2)3/2+(2)7/2 in the range of 37 ≤ ≤47. The process was studied in the presence and absence of a dc static electric field, also known as Förster resonances. The results show that even at high atomic density, two-body interaction dominates de process, despite the clear manifestation of Rydberg blockade. After several improvements in our experimental setup, we have studied also a Förster resonance peak 375/2+375/2393/2+357/2 as a function of the magnitude of the dc static electric field as well as the angle between this field and the longitudinal axis of the ODT. We discuss the results and future challenges of the experiment.
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Estudo de colisões atômicas ultrafrias: mecanismos de perda e espectroscopia de fotoassociação. / Investigation of ultracold atomic collisions: trap loss mechanisms and photoassociation spectroscopy.Telles, Gustavo Deczka 18 December 2002 (has links)
Neste trabalho, abordamos dois assuntos independentes e interessantes que permeiam o cotidiano dos pesquisadores da área de resfriamento e confinamento de átomos neutros. O primeiro está relacionado aos processos de perda de átomos ocorrendo em armadilhas magneto-ópticas, a partir das quais o fenômeno é observado. Mostramos que a conjunção de dois modelos tradicionais da literatura é capaz de gerar um modelo semiclássico e semi-analítico básico e robusto, capaz de reproduzir as características fundamentais dos resultados experimentais já obtidos, incluindo os mais recentes. Isto demonstra que os aspectos essenciais dos mecanismos de perda em armadilhas são, agora, bem compreendidos. O segundo assunto abordado aqui está relacionado à observação de moléculas diatômicas formadas em armadilhas magneto-ópticas. Nesse sentido, uma série de experimentos básicos foi realizada, gerando resultados e discussões que constituem uma rica fonte de informação inspirando a continuação e conclusão do trabalho iniciado aqui, cujo objetivo final é a caracterização precisa e o desenvolvimento técnicas de resfriamento e aprisionamento de moléculas diatômicas heteronucleares. / We report the results concerning to two main subjects of laser cooling and trapping community. We begin by presenting the results of modeling two-body trap loss rates as a function of the trap laser intensity. We show that one can merge two simple theories to obtain a semiclassical and semi-analytical model which is able to provide the fundamental properties observed in the experimental results found in the literature. Hence, we concluded that the essential features of the two-body trap loss rates taking place in MOTs are now well understood. On the other hand, we run a set of experiments trying to produce and detect heteronuclear diatomic ultracold molecules. Although this has not been accomplished yet, we have acquired a wide and rich amount of data that will certainly be very helpful for continuing and concluding the work here started. In the near future the photoassociation spectroscopy of ultracold heteronuclear diatomic molecules will provide valuable information to help in its manipulation.
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Estudo de Blindagem Óptica em Colisões Frias / Studies on Optical Shielding of Cold CollisionsMuniz, Sérgio Ricardo 05 March 1998 (has links)
Neste trabalho, mostramos que é possível suprimir a maioria dos processos inelásticos que podem causar perdas de átomos em armadilhas magneto-ópticas. Nossos resultados revelam que o processo de blindagem óptica (demonstrado pelo nosso grupo, pela primeira vez para o processo de ionização fotoassociativa Phys. Rev. Lett. 73, 1911 (1994)) é bem mais geral do que se supunha. Permitindo, inclusive, a supressão de colisões entre átomos no estado fundamental. E provavelmente qualquer outro processo inelástico que ocorra a curtas distâncias internucleares. Para se chegar a esses resultados, foi necessário desenvolver uma nova técnica de aprisionamento, que permite o estudo de colisões frias, mesmo em armadilhas cujo potencial de confinamento é pequeno. Graças a essa técnica foi possível, pela primeira vez, observar perdas causadas por mudança de estrutura hiperfina, numa armadilha de átomos de sódio operando na linha D1 (carregada a partir de uma célula de vapor). Essa técnica ainda nos permitiu medir a taxa de colisões frias () no trap da linha D1, um dado que até então não existia na literatura. Para verificar a confiabilidade dos resultados obtidos por essa técnica, realizamos também medidas de  na linha D2 e comparamos esses resultados com outros existentes na literatura (obtidos por uma técnica diferente). A boa concordância entre esses resultados nos deixa confiantes em dizer que essa técnica, além de ser muito interessante, no estudo de armadilhas rasas (seja isso devido à intensidade dos lasers de aprisionamento, seja devido a natureza própria da armadilha), é também bastante confiável / In this work, we showed that is possible to suppress most of the inelastic processes that may cause losses of atoms in a magneto-optical trap. Our results reveal that the process of optical shielding (demonstrated by our group, for the first time to photoassociative ionization - Phys. Rev. Lett. 73, 1911 (1994)) is much more general than it was supposed. Even allowing the suppression of ground state collisions and probably any other inelastic process that happens at short internuclear distances. To achieve those results, it was necessary to develop a new trapping technique, which allows the study of cold collisions, even in traps whose confinement potential is small. Thanks to that technique it was possible, for the first time, to observe losses caused by hyperfine changing collisions, in a trap of sodium atoms operating in the D1 line (loaded from a vapor cell). That technique has still allowed us to measure the rate of cold collisions () for the D1 line trap, a result which, until now, did not exist in the literature. To verify the reliability of the results obtained by that technique, we also accomplished measures of  in the D2 line and compared those results with other existent ones in the literature (obtained by a different technique). The good agreement among those results, made us confident in saying that this technique, besides being very interesting in the study of shallow traps (due to the intensity of the trapping lasers, or due to the own nature of the trap), it is also quite reliable.
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Exploring many-body physics with ultracold atomsLeblanc, Lindsay 18 November 2010 (has links) (PDF)
By exploiting the versatility of ultracold atoms experiments, a variety of many-body phe- nomena can be studied. Ferromagnetism in a trapped ultracold gas of repulsively interacting fermions is considered within a local-density approximation and beyond, where energetic sig- natures indicate its onset. Transport of a Bose-Einstein condensate is explored experimentally in a tunable double-well potential, and a crossover from hydrodynamic to Josephson transport is observed as the barrier between condensates is raised. To add a degree of freedom for the manipulation of ultracold gases, two schemes for species-specific optical lattices are developed theoretically.
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Landau-Zener transitions in noisy environment and many-body systemsSun, Deqiang 16 January 2010 (has links)
This dissertation discusses the Landau-Zener (LZ) theory and its application in
noisy environments and in many-body systems. The first project considers the effect
of fast quantum noise on LZ transitions. There are two important time intervals
separated by the characteristic LZ time. For each interval we derive and solve the
evolution equation, and match the solutions at the boundaries to get a complete
solution. Outside the LZ time interval, we derive the master equation, which differs
from the classical equation by a quantum commutation term. Inside the LZ time
interval, the mixed longitudinal-transverse noise correlation renormalizes the LZ gap
and the system evolves according to the renormalized LZ gap. In the extreme quantum
regime at zero temperature our theory gives a beautiful result which coincides
with that of other authors. Our initial attempts to solve two experimental puzzles
- an isotope effect and the quantized hysteresis curve of a single molecular magnet -
are also discussed.
The second project considers an ultracold dilute Fermi gas in a magnetic field
sweeping across the broad Feshbach resonance. The broad resonance condition allows
us to use the single mode approximation and to neglect the energy dispersion of the
fermions. We then propose the Global Spin Model Hamiltonian, whose ground state
we solve exactly, which yields the static limit properties of the BEC-BCS crossover. We also study the dynamics of the Global Spin Model by converting it to a LZ
problem. The resulting molecular production from the initial fermions is described
by a LZ-like formula with a strongly renormalized LZ gap that is independent of the
initial fermion density. We predict that molecular production during a field-sweep
strongly depends on the initial value of magnetic field. We predict that in the inverse
process of molecular dissociation, immediately after the sweeping stops there appear
Cooper pairs with parallel electronic spins and opposite momenta.
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From DNA bases to ultracold atoms : probing ensembles using supersonic beamsSmith, Valoris Reid 04 May 2015 (has links)
This thesis discusses two ensembles, the study of which was dependent upon the controllable production of cold gas-phase samples using supersonic beams. The experiments on DNA bases and base clusters were carried out in Germany at the Max Born Institute. The experiments anticipating the construction of a molecular beam slower were carried out in the United States at the University of Texas at Austin. Femtosecond pump-probe techniques were employed to study the dynamics and electronic character of DNA bases, pairs and clusters in the gas phase. Experiments on DNA base monomers confirmed the dominance of a particular relaxation pathway, the nπ* state. Competition between this state and another proposed relaxation pathway was demonstrated through observations of the DNA base pairs and base-water clusters, settling a recent controversy. Further, it was determined that the excited state dynamics in base pairs is due to intramolecular processes rather than intermolecular processes. Finally, results from base-water clusters confirm that microsolvation permits comparison with biologically relevant liquid phase experiments and with ab initio calculations, bridging a long-standing gap. A purely mechanical technique that does not rely upon quantum or electronic properties to produce very cold, very slow atoms and molecules would be more generally applicable than current approaches. The approach described here uses supersonic beam methods to produce a very cold beam of particles and a rotating paddle-wheel, or rotor, to slow the cold beam. Initial experiments testing the possibility of elastic scattering from a single crystal surface were conducted and the implications of these experiments are discussed. / text
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Quantum Control and Quantum Chaos in Atomic Spin SystemsChaudhury, Souma January 2008 (has links)
Laser-cooled atoms offer an excellent platform for testing new ideas of quantum control and measurement. I will discuss experiments where we use light and magnetic fields to drive and monitor non-trivial quantum dynamics of a large spin-angular momentum associated with an atomic hyperfine ground state. We can design Hamiltonians to generate arbitrary spin states and perform a full quantum state reconstruction of the results. We have implemented and verified time optimal controls to generate a broad variety of spin states, including spin-squeezed states useful for metrology. Yields achieved are of the range 0.8-0.9.We present a first experimental demonstration of the quantum kicked top, a popular paradigm for quantum and classical chaos. We make `movies' of the evolving quantum state which provides a direct observation of phase space dynamics of this system. The spin dynamics seen in the experiment includes dynamical tunneling between regular islands, rapid spreading of states throughout the chaotic sea, and surprisingly robust signatures of classical phase space structures. Our data show differences between regular and chaotic dynamics in the sensitivity to perturbations of the quantum kicked top Hamiltonian and in the average electron-nuclear spin entanglement during the first 40 kicks. The difference, while clear, is modest due to the small size of the spin.
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Formation of molecules in ultra-cold atomic gazes via quasi-resonant fieldsSokhoyan, Ruzan 07 June 2010 (has links) (PDF)
We study the nonlinear mean-field dynamics of diatomic molecule formation at coherent photo- and magneto-association of ultracold atoms focusing on the case when the system is initially in the all-atomic state. We show that in the limit of strongly nonlinear interaction between an ultra-cold atomic-molecular system and a quasi-resonant electromagnetic field, the molecule formation process, depending on the characteristics of the associating field, may evolve according two different scenarios, namely, weak- and strong-oscillatory regimes. In the first case the number of molecules increases without pronounced oscillations of atom-molecule populations, while in the second case high-amplitude Rabi-type oscillations arise. Assuming an arbitrary external field configuration, we construct analytical solutions to describe the system's temporal dynamics in the both interaction regimes. Further, we investigate the influence of inter-particle elastic scattering on the dynamics of coherent molecule formation subject to an external field configuration of the resonance-crossing Landau-Zener model. We derive an approximate solution which for the first time describes the whole temporal dynamics of the molecule formation in this general case.
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