This thesis deals with the reconstruction of a MOTRe- Mi apparatus, which represents the combination of a magneto-optical trap (MOT) and a Reaction Microscope (ReMi). With this setup an ultracold degenerate Fermi gas consisting of 6Li atoms will be generated and studied in future. Primarily the Li atoms will be vaporized, precooled in a Zeeman Slower, trapped and stored with the MOT at typical temperatures of a few 100 μK. Within the scope of this thesis initially the parameters of the Zeeman Slower were optimized. For this purpose the magnetic field profiles of the single coils were measured and the ideal coil currents determined. The efficiency and other properties of the Zeeman Slower were calculated with a simulation programme. The focus of this thesis was on planning and reconstructing the laser system and the optical setup for the magneto-optical trap. This included among others the adaptation of the laser frequencies from 7Li to 6Li and the integration of an additional amplifier in order to achieve a higher output power. Using the frequency stabilization scheme of a frequency offset lock ([SEG+99]) it is now possible to tune the laser frequency over a large range at a constant laser power. This is required on the one hand for the later transfer of the atoms to a dipole trap and on the other hand for the imaging of the atom cloud by light absorption at high magnetic fields. Finally the vacuum chamber and the Reaction microscope was baked out and activated at a vacuum of about 7 · 10-10 mbar.
This thesis deals with the reconstruction of a MOTRe- Mi apparatus, which represents the combination of a magneto-optical trap (MOT) and a Reaction Microscope (ReMi). With this setup an ultracold degenerate Fermi gas consisting of 6Li atoms will be generated and studied in future. Primarily the Li atoms will be vaporized, precooled in a Zeeman Slower, trapped and stored with the MOT at typical temperatures of a few 100 μK. Within the scope of this thesis initially the parameters of the Zeeman Slower were optimized. For this purpose the magnetic field profiles of the single coils were measured and the ideal coil currents determined. The efficiency and other properties of the Zeeman Slower were calculated with a simulation programme. The focus of this thesis was on planning and reconstructing the laser system and the optical setup for the magneto-optical trap. This included among others the adaptation of the laser frequencies from 7Li to 6Li and the integration of an additional amplifier in order to achieve a higher output power. Using the frequency stabilization scheme of a frequency offset lock ([SEG+99]) it is now possible to tune the laser frequency over a large range at a constant laser power. This is required on the one hand for the later transfer of the atoms to a dipole trap and on the other hand for the imaging of the atom cloud by light absorption at high magnetic fields. Finally the vacuum chamber and the Reaction microscope was baked out and activated at a vacuum of about 7 · 10-10 mbar.
Within the MOTREMI experiment at the Max-Plank-Institut für Kernphysik a new optical trap was constructed. A already installed magneto-optical trap cools 6Li atoms down to temperatures on the order of 100 μK. From the corresponding atoms an ultracold lithium gas is trapped inside the center of the main vacuum chamber. In the further course of the experiment, ionization measurements with a degenerate quantum gas will be carried out. In order to create theses gases, one needs to surpass the temperature limit of the magneto-optical trap. Traps using a high intensity, far red-detuned focused laser beam are able to achieve temperatures on the order of 100 nK. An intensity stabilization which is able to extend the lifetime of trapped gas was constructed in the scope of this thesis. With the use of two different photodiodes, every intensity level of the laser is covered. The high laser powers which are needed for the trap, can lead to thermal effects in the entire setup. Consequently, the properties of the laser and the optical elements the laser is passing through can change. Therefore, a quantitative analysis of these thermal effects has been carried out. Besides the shift and reduction of the focused laser beam, the thermal effect on the trap size was obtained.
During my PhD, I participated in the full setup from scratch of an experiment that aims at cooling down and manipulating two fermionic alkaline atomic species, 6Li and 40K. Our goal is to study ultracold Fermi mixtures with mass imbalance, and to realize a flexible quantum analog simulator. In fact, for certain quantum many-body problems, such as high critical temperature superconductivity and frustrated anti-ferromagnetism, there is neither complete analytical nor numerical solution. Therefore, cold atoms systems, due to their purity and their high degree of tunability, even on their interaction itself, offer an interesting complementary point of view in the study of those phenomena. As far as the experimental setup is concerned, we built an ultra-high vacuum system, a complete and stable laser source for each species, as well as two performing atomic sources, a 6Li Zeeman slower and a 40K bidimensionnal magneto-optical trap; most of the optical and electrical quantities, as well as the imaging diagnostics, being computer controlled. Once those preliminary steps have been performed and optimized, we could obtain an efficient double magneto-optical trap, containing typically 5x10^9 atoms of 6Li and 8x10^9 atoms of 40K. In this configuration, we produced the first 6Li40K* heteronuclear molecules by photoassociation, for which we identified 70 rovibrational lines. In a second part, I describe in detail the magnetic transport of the atomic mixture, between the magneto-optical trap chamber and a science cell, located in an ultra-high vacuum region with large optical access. The complete setup, from its design to its experimental implementation and optimization, as well as the development of the program and the useful numerical diagnostics, are the heart of my work. The transport efficiency could be tested and optimized, allowing for an efficient transfer of the mixture in the science cell. Thus, after this thesis, all the experimental tools are operational in order to allow for evaporative cooling of the mixture in an optically plugged magnetic trap. Therefore, the field is open for quantum simulation and understanding of many-body problems in ultracold Fermi mixtures.
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.
A new experiment is being built at the Max-Planck-Institut für Kernphysik (MPIK) within the PRIOC project (Precision studies on Ion Collisions) where a reaction microscope (Remi) and a magneto-optical trap (MOT) as target are combined to a so called MOTRemi. This setup will be implemented into the ion storage ring 'Testspeicherring' (TSR) of the MPIK. The world-wide unique combination of these three state-of-the-art technologies shall enable to perform kinematically complete studies of ion-atom collision with unprecedented detail and resolution. In this thesis, a two-dimensional magneto-optical trap (2D-MOT) was developed and tested as a source of slow lithium atoms for the loading of the target MOT. This method allows a very compact setup and oers a collimated beam and a ux of cold atoms comparable to the highest uxes achieved by using laser cooling. The temperature of the atomic beam was determined to be at the scale of a few Kelvin and, thus, it is already an adequate stand-alone target for momentum resolved experiments.
This thesis reports on the construction of an apparatus capable of producing a molecular Bose-Einstein-Condensate (BEC) of 6Li2. To create a condensate fermionic lithium is first evaporated in an oven, slowed by a Zeeman slower and captured in a magneto-optical-trap (MOT). A scheme for creating time-averaged arbitrary optical potentials for optimized transfer of the atoms from the MOT to a high-power, far detuned optical dipole trap was implemented, as well as magnetic field coils to tune the interactions of the atoms via Feshbach resonances. The first experiments with the new machine include the characterization of the optical dipole trap and evaporative cooling of 6Li.
Simulating highly correlated quantum systems with classical computers exceed their capa- bilities as the system size increases. In analog quantum simulators, the system of interest is mimicked by another quantum system in a highly controllable and accessible environ- ment. Even though quantum simulations with ultracold atoms have been demonstrated successfully, ultra-low temperature regimes are experimentally challenging to achieve and still remain to be explored. New approaches to realizing ever lower temperatures, especially in Fermi systems, have been and continue to be a constant pursuit in Atomic, Molecular, and Optical Physics (AMO). Within this thesis, a new quantum gas experiment of fermionic 6Li and bosonic 166Er is presented and first results on sympathetic cooling of Li to quantum degeneracy by Er are demonstrated. The experimental apparatus is described in detail with a focus on the Li subsystem of the dual-species experiment. Standard and further developed laser cooling techniques used to produce a Magneto-Optical Trap (MOT) of Li are characterized, along with their associated vacuum system stages. In this context, a combined Optical Pumping / Transversal Cooling (OP/TC) technique of the atomic beam on the D1-line is presented, and an enhancement of the MOT loading rate by one order of magnitude is demonstrated. The architecture and building blocks of the laser system for providing resonant light at 671 nm for laser cooling of Li are detailed, and laser locking techniques for frequency stabilization and light amplification by injection locking of high-power laser diodes are presented. Special focus is placed on the introduction and characterization of a new laser- diode-independent injection locking technique, keeping spectrally pure amplified light by a periodic slave current optimization routine executed by a microcontroller. The system has been submitted for patent approval. In further steps of optical cooling of Li, a non-standard free-space Gray Molasses (GM) technique based on intensity ramps, providing temperatures as low as 13 µK, is presented. The non-standard technique is characterized and compared to the standard pulse GM approach, which typically achieves 50 µK only. Cooling steps for preparing an ultracold Li cloud in the glass cell start from an Optical Dipole Trap (ODT) loaded by a compressed Magneto-Optical Trap (cMOT) and consecutive evaporation into a 1D transport lattice of counter propagating 1064 nm laser beams. By detuning one of the lattice beams, optical transport over 1 m to the glass cell with an efficiency of 74% is demonstrated. In a combined ErLi sequence, the two species are transported to the glass cell together and loaded to 1064 nm ODTs. Sympathetic cooling of Li by forced evaporation of Er to T/TF = 0.77 ± 0.10 next to the production of an Er BEC are presented. To conclude, this work introduces a new promising dual-species quantum gas experiment and its ability for providing sympathetic cooling of Li by Er to quantum degeneracy is demon- strated. These findings are an encouraging foundation for achieving higher degeneracies by refined experimental control in pursuit of penetrating unexplored temperature regimes in quantum simulators.