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Experimental advances toward a compact dual-species laser cooling apparatusLadouceur, Keith 05 1900 (has links)
This thesis describes the advances made towards a dual-species magneto-optical trap (MOT) of Li and Rb for use in photoassociation spectroscopy, Feshbach resonance studies, and, as long-term aspirations, the formation of ultracold heteronuclear polar molecules. The initial discussion will focus on a brief theoretical overview of laser cooling and trapping and the production of ultracold molecules from a cold atom source. Subsequently, details of the experimental system, including those pertaining to the required laser light, the vacuum chamber, and the computer control system will be presented. Finally, preliminary optimization and characterization measurements showing the performance of a single species Li MOT are introduced. These measurements demonstrated the loading of over 8 x 107 Li atoms directly into a MOT without the need for a Zeeman slower.
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Experimental advances toward a compact dual-species laser cooling apparatusLadouceur, Keith 05 1900 (has links)
This thesis describes the advances made towards a dual-species magneto-optical trap (MOT) of Li and Rb for use in photoassociation spectroscopy, Feshbach resonance studies, and, as long-term aspirations, the formation of ultracold heteronuclear polar molecules. The initial discussion will focus on a brief theoretical overview of laser cooling and trapping and the production of ultracold molecules from a cold atom source. Subsequently, details of the experimental system, including those pertaining to the required laser light, the vacuum chamber, and the computer control system will be presented. Finally, preliminary optimization and characterization measurements showing the performance of a single species Li MOT are introduced. These measurements demonstrated the loading of over 8 x 107 Li atoms directly into a MOT without the need for a Zeeman slower.
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Experimental advances toward a compact dual-species laser cooling apparatusLadouceur, Keith 05 1900 (has links)
This thesis describes the advances made towards a dual-species magneto-optical trap (MOT) of Li and Rb for use in photoassociation spectroscopy, Feshbach resonance studies, and, as long-term aspirations, the formation of ultracold heteronuclear polar molecules. The initial discussion will focus on a brief theoretical overview of laser cooling and trapping and the production of ultracold molecules from a cold atom source. Subsequently, details of the experimental system, including those pertaining to the required laser light, the vacuum chamber, and the computer control system will be presented. Finally, preliminary optimization and characterization measurements showing the performance of a single species Li MOT are introduced. These measurements demonstrated the loading of over 8 x 107 Li atoms directly into a MOT without the need for a Zeeman slower. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
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Ultracold dipolar gases of NaCs ground state moleculesLam, Aden Zhen Hao January 2022 (has links)
Ultracold bialkali polar molecules present a wealth of opportunities in quantum science research and technology; including fields such as quantum simulation, quantum chemistry, quantum metrology, precision measurement and quantum computation. A great deal of interest lies in their rich internal rotational and vibrational state structure and their large electric dipole moment. However, the additional complexity also provides significant challenges. To date, only a limited number of molecular species are available at ultracold temperatures below 1 microkelvin. The assembly of heteronuclear ground state molecules from ultracold atoms has emerged as a promising approach for creating ultracold molecules. In this thesis, I will present the creation of the first ultracold gases of NaCs ground state molecules. First, we produce an ultracold mixture of Na and Cs. Second, we associate weakly bound molecular pairs from the Na-Cs mixture. Finally, we apply a two-photon stimulated Raman adiabatic passage (STIRAP) pulse to transfer the weakly bound NaCs molecules into the deeply bound rovibrational ground state.
I report on the construction of a new apparatus that produces ultracold mixtures of Na and Cs. We use this apparatus to assemble weakly bound NaCs molecules and successfully transfer up to 20,000 ultracold dipolar NaCs molecules to their rovibrational ground state in each experimental run. On the way to these results, we demonstrated a pathway towards creating the first quantum degenerate mixtures of Na and Cs. We identified and characterized an interspecies Feshbach resonance at 864.12(5) G, adiabatically sweeping across it to form weakly bound NaCs Feshbach molecules. We characterized the Feshbach molecule formation in various parameter regimes. Next, we performed a study of accessible NaCs excited states and identified a pathway to the rovibrational ground state using one- and two-photon spectroscopy. Finally, we demonstrated STIRAP to the rovibrational ground state, and investigated basic properties of the ground state molecules.
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The strontium molecular lattice clock: Vibrational spectroscopy with hertz-level accuracyLeung, Kon H. January 2023 (has links)
The immaculate control of atoms and molecules with light is the defining trait of modern experiments in ultracold physics. The rich internal degrees of freedom afforded by molecules enrich the toolbox of precision spectroscopy for fundamental physics, and hold great promise for applications in quantum simulation and quantum information science. A vibrational molecular lattice clock with systematic fractional uncertainty at the 14th decimal place is demonstrated for the first time, matching the performance of the earliest optical atomic clocks. Van der Waals dimers of strontium are created at ultracold temperatures and levitated by an optical standing wave, whose wavelength is finely tuned to preserve the delicate molecular vibrational coherence.
Guided by quantum chemistry theory refined by highly accurate frequency-comb-assisted laser spectroscopy, record-long Rabi oscillations were demonstrated between vibrational molecular states that span the entire depth of the ground molecular potential. Enabled by the narrow molecular clock linewidth, hertz-level frequency shifts were resolved, facilitating the first characterization of molecular hyperpolarizability in this context. In a parallel effort, deeply bound strontium dimers are coherently created using the technique of stimulated Raman adiabatic passage. Ultracold collisions of alkaline-earth metal molecules in the absolute ground state are studied for the first time, revealing inelastic losses at the universal rate.
This thesis reports one of the most accurate measurement of a molecule's vibrational transition frequency to date, which may potentially serve as a secondary representation of the SI unit of time in the terahertz (THz) band where standards are scarce. The prototypical molecular clock lays the important groundwork for future explorations into THz metrology, quantum chemistry, and fundamental interactions at atomic length scales.
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Reaching the Bose-Einstein Condensation of Dipolar Molecules: a Journey from Ultracold Atoms to Molecular Quantum ControlBigagli, Niccolò January 2024 (has links)
Achieving the quantum control of ever more complex systems has been a driving force of atomic, molecular, and optical physics. This goal has materialized in the harnessing of systems with increasingly rich structures and interactions: the more sophisticated the system, the more faceted and fascinating its application to fields as varied as quantum simulation, quantum information, many body physics, metrology, and quantum chemistry. One of the current frontiers of quantum control is ultracold dipolar molecules. They present rich internal structures and long-range, anisotropic dipole-dipole interactions which promise to revolutionize AMO physics, for example by realizing realistic Hamiltonians in quantum simulation, by providing a new platform for quantum information, and by achieving a novel kind of quantum liquid.
Despite its promises, the full quantum control of dipolar molecules has been over a decade in the making. The difficulties in either directly laser cooling molecules or in collisionally stabilizing their bulk samples have been major roadblocks that have hampered the development of this quantum system. The realization of a Bose-Einstein condensate of dipolar molecules has been a particularly elusive milestone. In this thesis, I report on the first observation of this quantum state of matter.
The work that brought us to this achievement parallels the historical evolution of AMO physics in the last thirty years. To reach a BEC of molecules, we initially constructed a dual species experiment capable of realizing the simultaneous Bose-Einstein condensation of atomic sodium (Na) and cesium (Cs). Individual BECs of sodium and cesium were first reported in 1995 and 2003 respectively, while our experiment was the first instance of their concurrent condensation. The study of the Na-Cs interatomic scattering properties in an homogeneous magnetic field showed us the path to the Feshbach association of loosely-bound sodium-cesium (NaCs) molecules, a technique first demonstrated in 2006 for heteronuclear molecules but never attempted on our species. Following the Feschbach association, we determined a novel pathway to the molecular electronic, vibrational and rotational ground state using STIRAP.
From this point, we found ourselves at the forefront of the field: bulk samples of bosonic molecules such as NaCs had neither been stabilized against collisional losses nor evaporatively cooled. At first, we successfully applied a single-frequency microwave shielding approach to decrease in-bulk losses by a factor of 200 and reach lifetimes on the order of 2 s, allowing us to measure high elastic scattering rates and characterize their dipolar anisotropy. Moreover, we demonstrated the first evaporative cooling of a bosonic molecular gas by increasing its phase-spacedensity by a factor of 20 and reaching a temperature of 36(5) nK. Since this proved insufficient to achieve Bose-Einstein condensation due to unexpected three-body losses, we introduced an enhanced microwave shielding technique, double microwave shielding. This further decreased loss rates enabling efficient evaporative cooling of our sample to a long-lived Bose-Einstein condensate of dipolar molecules. This new double microwave shielding technique also allows the tunability of the strength of dipole-dipole interaction, establishing ultracold bosonic dipolar molecules as a new quantum liquid for the exploration of many body physics.
In addition to the experimental work on dipolar NaCs, we have theoretically explored the field of direct molecular laser cooling. Our aim was twofold: we aimed to expand the category of molecules that can be laser cooled and to simplify the identification of laser cycling schemes. For the former goal, we lifted the widespread assumption that only molecules with diagonal Franck-Condon factors could be laser cooled. For the latter, we decided to employ publicly available repositories of molecular transitions. A second consequence of the use of these databases is that they contain data on molecules of interest to other scientific fields, further establishing direct laser cooling as a technique that could be of interest beyond AMO physics. Our work was successful in that we identified laser cycling schemes for C₂ and OH+. To simplify the determination of laser cycling schemes, we developed a graph-based algorithm form their identification starting from spectroscopic data.
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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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Contrôle par laser de la formation de molécules polaires paramagnétiques ultra-froides / Laser control of the formation of ultracold paramagnetic polar moleculesDevolder, Adrien 08 October 2019 (has links)
La thèse se positionne dans le domaine des molécules ultra-froides, c’est-à-dire des molécules qui ont des vitesses correspondant à des températures de l’ordre du µK. L’obtention de gaz dilués moléculaires à ces températures peut ouvrir la porte à des applications importantes en simulation ou en informatique quantique. La thèse s’intéresse plus particulièrement à la formation de molécules dipolaires électriques et magnétiques. Celles-ci sont présagées pour être un système idéal dans l’optique d’un simulateur quantique du système réseau-spin, permettant de décrire le magnétisme dans les solides. Nous avons choisi l’exemple de la molécule RbSr qui fait l’objet actuellement d’une expérience à Amsterdam. Nous avons donc exploré plusieurs alternatives basées sur l’emploi de laser pour la formation de molécules RbSr ultra-froides Nous avons d’abord considéré la photoassociation dont le principe est de coupler l’état de collision initial avec un état rovibrationnel d’un état électronique excité. L’étape d’émission spontanée qui suit forme des molécules dans l’état électronique fondamental. Nous avons également considéré le problème des pertes supplémentaires d’atomes lorsque le laser de photoassociation est intense et focalisé, mises en évidence dans une expérience à Bangalore. Dans la suite de la thèse, nous avons exploré des méthodes cohérentes. Nous avons montré que des molécules faiblement liées de RbSr peuvent être formées à l’aide d’un STIRAP en partant de paires d’atomes isolées et confinées dans un isolant de Mott. Nous avons ensuite étudié leur stabilisation vers le niveau le plus profond de l’état fondamental de la molécule à l’aide d’un second STIRAP. Enfin, nous avons étudié des méthodes se déroulant uniquement dans l’état électronique fondamental. La formation est induite par l’utilisation d’une impulsion à dérive de fréquence induisant un passage adiabatique ou à l’aide d’une impulsion-pi. En plus, nous avons découvert que cette méthode formation peut être reliée à une résonance de Feshbach dans la représentation habillée par les photons, que nous avons appelée Résonance de Feshbach auto-induité assistée par Laser (LASIFR en anglais). Nous montrons qu’elles sont un outil prometteur et puissant pour le contrôle des propriétés de mélange de gaz d’atomes ultra-froids, comme par exemple la longueur de diffusion. / The thesis is positioned in the ultracold domain, i.e molecules which have velocities corresponding to microkelvin temperatures. The formation of molecular diluted gas at these temperatures is promising for important applications in quantum simulation, quantum information or in precision measurements.More particularly, the thesis is focused on the formation of molecules which are polar and paramagnetic. Some recent works are predicted that these molecules could be the ideal system for creating a quantum simulator of the lattice-spin system, which can describe the magnetism in solids. We have chosen the example of RbSr molecules for whose an experience runs in Amsterdam. We explored some alternatives based on the use of lasers for the formation of ultracold RbSr molecules.First, we considered the photoassociation whose the principle is coupling the initial scattering state with a rovibrational level of an excited electronic state. The following spontaneous emission step creates molecules in the electronic ground state. We also considered the problem of atom losses observed by experiments in Bangalore, when a focused photoassociation laser is applied. In the rest of the thesis, we explored coherent methods. Firstly, we showed a STIRAP sequence could create weakly bound molecules from isolated atomic pairs confined in a Mott insulator. Lastly, we explored some of these methods where the dynamic occurs only in the electronic ground state. The formation is induced by the use of a chirped pulse or a pi-pulse. We studied the factors of the transfer. Moreover, we discovered this method is related to a new kind of Feshbach resonances in the photon dressed picture, called Laser Assisted Self-Induced Feshbach Resonance (LASIFR). We showed LASIFR present the advantages of Magnetic and Optical Feshbach Resonances. They are a promising and powerful tool for the control of properties of quantum gas mixtures, like the interspecies scattering length.
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Étude théorique de collisions inélastiques atome – diatome sous l’action d’un champ magnétique : applications en Astrochimie et au domaine du refroidissement et du piégeage moléculaires / Theoretical studies of atom - diatom inelastic collisions under magnetic field : applications in Astrochemistry and in the field of molecular cooling and trappingTurpin, Florence 17 December 2010 (has links)
D’immenses progrès ont été réalisés ces dernières années dans le champ de production de condensats de Bose-Einstein moléculaires pour l’obtention et le piégeage de molécules ultrafroides ioniques et neutres. Ces échantillons de molécules ultrafroides trouvent des applications dans des domaines très variés tels que les mesures pectroscopiques de haute précision ou bien encore le stockage de l’information quantique. La volonté d’optimiser les procédés de refroidissement et des techniques de piégeage a stimulé un grand nombre d’études théoriques. La plupart de ces études sont dédiées au refroidissement des molécules en collision avec un gaz tampon (3 He). La surface d’énergie potentielle de l’état fondamental du complexe de van der Waals He–MnH(X7Σ+) est présentée, suivie du calcul des états liés correspondant au complexe ainsi que l’étude de la relaxation Zeeman associée au système en fonction du champ magnétique appliqué. Dans le domaine de l’astrochimie, l’étude de la désexcitation rotationnelle de CH+ en collision avec l’hélium est également présentée. / Tremendous progress in experimental production and trapping of ultracold neutral and ionic molecules has been achieved over the past few years which even allowed the production of molecular Bose–Einstein condensates. These ultracold molecules samples have potential applications in many different fields, such as precision spectroscopic measurements or quantum information storage and processing. The optimization of the cooling processes and the trapping techniques also stimulated a great number of theoretical studies. Many of them are dedicated to inelastic scattering of molecules in collisions with 3He atoms (buffer gas cooling method). The potential energy surface of the ground state of the He–MnH(X7Σ+) van der Waals complex is presented, followed by the calculations of the bound states of this system and the Zeeman relaxation in function of the magnetic field. In the field of astrochemistry, a quantum mechanical investigation of rotational energy transfer in cold collisions of CH+ with 4He atoms is presented.
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Formation of molecules in ultra-cold atomic gazes via quasi-resonant fields / Formation de molécules dans des gaz atomiques ultra-froids par des champs quasi-résonnantsSokhoyan, Ruzan 07 June 2010 (has links)
Nous étudions la dynamique non linéaire en champ moyen de la formation de molécules diatomiques par photo-association ou magnéto-association d’atomes ultra froids pour un système entièrement atomique dans l’état initial. Nous montrons que dans la limite d’une forte interaction non linéaire entre un système atome-molécule ultra froid et un champ électromagnétique quasi résonnant, le processus de formation du condensat moléculaire peut évoluer suivant deux scénarios en fonction des caractéristiques du champ : régime faiblement oscillatoire ou régime fortement oscillatoire. Dans le cas du régime faiblement oscillatoire, le nombre de molécules augmente sans oscillations prononcées des populations atomiques et moléculaires alors que de fortes oscillations de Rabi apparaissent dans le second cas. Nous présentons des solutions analytiques décrivant la dynamique temporelle du système dans ces deux cas. Nous étudions ensuite l’influence de la diffusion élastique entre particules sur la dynamique de formation cohérente de molécules sous l’action d’un champ extérieur représenté par le modèle de Landau-Zener. Nous déterminons une solution approchée qui décrit bien toute la dynamique temporelle de formation moléculaire dans ce cas général. / 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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