In this work we document the first measure of Feshbach resonances in our laboratory utilizing potassium 39 in the state F = 1, mF = 0. We submitted the 39K atoms trapped in an optical trap to a homogeneous magnetic field in the range of up to 800 Gauss, where are expected resonances for the species in the |F = 1› manifold. Those are the first steps to come up with a machine capable of using this technique for different and innovative studies on superfluidity in a mixture of quantum gases. In our case, we use the same pair of coils both to obtain different magnetic field gradients (phase of MOT and MT), in anti-Helmholtz configuration, as well as to obtain a homogeneous magnetic field (tuning the magnetic field around previewed resonance), in Helmholtz configuration. To make this possible, we have implemented a H-Bridge system, which consists in installing one of the coils in a system of power switches. We have prepared the atomic cloud since the MOT, passing through a Gray Molasses stage and reaching our Optical Dipole Trap with 106 atoms at 12 μK where we apply a homogeneous field and perform a loss spectroscopy. Here we will present the resonances we have obtained and its characterization.
In this work we document the first measure of Feshbach resonances in our laboratory utilizing potassium 39 in the state F = 1, mF = 0. We submitted the 39K atoms trapped in an optical trap to a homogeneous magnetic field in the range of up to 800 Gauss, where are expected resonances for the species in the |F = 1› manifold. Those are the first steps to come up with a machine capable of using this technique for different and innovative studies on superfluidity in a mixture of quantum gases. In our case, we use the same pair of coils both to obtain different magnetic field gradients (phase of MOT and MT), in anti-Helmholtz configuration, as well as to obtain a homogeneous magnetic field (tuning the magnetic field around previewed resonance), in Helmholtz configuration. To make this possible, we have implemented a H-Bridge system, which consists in installing one of the coils in a system of power switches. We have prepared the atomic cloud since the MOT, passing through a Gray Molasses stage and reaching our Optical Dipole Trap with 106 atoms at 12 μK where we apply a homogeneous field and perform a loss spectroscopy. Here we will present the resonances we have obtained and its characterization.
In this work we document the first measure of Feshbach resonances in our laboratory utilizing potassium 39 in the state F = 1, m F = 0. We submitted the 39K atoms trapped in an optical trap to a homogeneous magnetic field in the range of up to 800 Gauss, where are expected resonances for the species in the |F = 1 manifold.Those are the first steps to come up with a machine capable of using this technique for different and innovative studies on superfluidity in a mixture of quantum gases.In our case, we use the same pair of coils both to obtain different magnetic field gradients (phase of MOT and MT), in anti-Helmholtz configuration, as well as to obtain a homogeneous magnetic field (tuning the magnetic field around previewed resonance), in Helmholtz configuration.To make this possible, we have implemented a H-Bridge system, which consists in installing one of the coils in a system of power switches.We have prepared the atomic cloud since the MOT, passing through a Gray Molasses stage and reaching our Optical Dipole Trap with 10 6 atoms at 12 µK where we apply a homogeneous field and perform a loss spectroscopy.Here we will present the resonances we have obtained and its characterization.
In this thesis, we produce a Bose-Einstein condensate of sodium atoms in a magnetic plugged trap and in an optical dipole trap. First, we investigate the critical velocity by moving an obstacle through the condensate, comparing the result obtained with the the sound velocity. We make use of the critical velocity value to determine the rigth parameters to stir the condensate and nucleate quantized vortices, by introducing angular with the rotation of the srirring beam the number of vortices increases linearly until the rigid-body limit. In the second part we introduce potassium atom in the science chamber where from the begining of the MOT stage are observed ligth induced losses. In a single-specie operation we are able to cool down the potassium atoms by implementing the gray molasses technique, increasing its phase-space density in order have a good tranference efficienty to the magnetic trap. We also present the the sympathetic cooling of the K atoms due by elastic collision between the atomic species.
The possibility to mould and control pure quantum systems has been offered by the experimental observation of Bose-Einstein condensation, a unique phase of matter when macroscopic quantities of a gas occupy the lowest quantum state. Techniques for creating these degenerate gases vary from laboratory to laboratory; each offers an unique test bed for studying quantum physics on a macroscopic scale. This thesis reports on the experimental design, construction and performance of an apparatus to create two-component 87Rb and 41K condensates for studies of non-equilibrium dynamics. This thesis is broken down as follows. In Chapter 1, a brief overview of the history and status of Bose Einstein condensates is presented, to affirm the motivation behind our work. Chapter 2 then presents the fundamental theory and background information to understand how and why our experiment was built. Chapter 3 describes the bulk of the work undertaken at the beginning of this thesis. In particular it describes the design choices, construction and performance of the vacuum, and laser and magnetic coil systems that are the key structural elements of the apparatus. In particular the vacuum system is a two-component differentially pumped system designed to optimise the number and lifetime of trapped atoms. Another integral element of the vacuum chamber is the science cell that enables high optical access, and close physical, access to an atomic cloud. As a result, high resolution imaging, ≃ 980 nm resolution at 780 nm is expected with a commercial microscope objective lens. The laser system is carefully de- signed to best combine and deliver the seven different optical frequencies required to simultaneously trap and manipulate 87Rb and 41K atoms. The magnetic coil system also represents an integral component of the apparatus, responsible for trapping and transferring atoms in a quadrupole field. One pair of coils is able to have their current direction reversed in order to generate bias fields. This allows access to Feshbach resonances between the two species, once they have been condensed. The second part of this thesis, Chapter 4, describes the performance of the apparatus when used to simultaneously trap 41K and 87Rb in the 3D magneto- optical trap (MOT) and produce a condensate of 87Rb atoms. In particular 1 × 109 rubidium atoms are routinely trapped in the 3D-MOT and transferred to the science chamber. In the hybrid trap the atoms are evaporatively cooled via microwave radiation, later to be used to sympathetically cool 41K, and loaded into a hybrid optical dipole and magnetic trap. At this stage ≃ 5 × 106 atoms are evaporatively cooled, by lowering the trap depth of the optical dipole beam, until a condensate of 87Rb is formed, containing 1.5 × 105 atoms. Additionally we are able to produce 3D MOTs of 41K simultaneously with the 87Rb 3D MOTs.
Research on degenerate quantum gases of dilute atomic gases has become a well established field in modern physics and revealed many astonishing phenomena. The first experiments on Bose and Fermi gases at low temperatures aimed to prove the predictions of quantum mechanics on a macroscopic scale. Since then we make use of Bose and Fermi gases and mixtures of any combination to model other many body systems. A property of Bose Einstein condensates is superfluidity which we want to investigate further in toroidal potentials with a new apparatus which can produce an all-optical BEC. This means trapping thermal atoms in an optical dipole trap and cooling the sample by evaporation into the quantum degenerate regime. This new technique was first successfully demonstrated by M.D. Barrett et al. in 2001 and promises to be faster and simpler than the well established and common way of evaporation in magnetic traps. A new apparatus was built by the author and we report on the experimental details of the trapping of 87Rb atoms from a hot vapour and cooling them in a magneto-optical trap, and further evaporation to quantum degeneracy in a crossed optical dipole trap operating at a wavelength of l = 1064nm, with accurate control of the power in both beams via a feedback loop. The evaporation of neutral atoms of 87Rb in far red detuned optical dipole traps using linearly polarised laser light is spin independent, and mixed spinor condensates of the F=1 manifold can be formed. As an empirical technique we found by applying a magnetic gradient field during the final evaporation that we can selectively populate mF spin states or prepare mixtures. This intriguing mechanism was found earlier as well by M. S. Chang, but is yet not fully understood and subject of our future research. We can now routinely prepare an almost pure condensate containing up to 7000 atoms in the condensed phase purely in the mF = 0 spin state. This thesis contains the theoretical framework of Bose-Einstein condensation with in mean-field theory, the concepts of cooling of atoms in magneto-optical traps, the trapping and evaporation in optical dipole traps and the experimental realisation. In the future this experiment will be extended by a fast scanning dipole trap to apply arbitrary time averaged potentials of more complex geometries, such as toroidal traps to study the effects of superfluidity in a periodic potential. The production of toroidal traps and cold atoms in such a trap are outlined in this thesis.
Two-component fluids can be miscible (if they overlap in space) or immiscible (if they remain phase-separated). In the context of trapped two-species Bose-Einstein condensates (BECs), these miscibility regions can only be fully characterize if one considers the interspecies interaction, the mass ratio and the number of atoms in each species. The dynamics of coupled vortices is different for each miscibility region and exotic vortices configurations (such as, square vortex lattices, \"vortex sheets\", skyrmions, etc.) are expected to occur. In this thesis, we present the construction of a new experimental system able to produce a two-species Bose-Einstein condensate of 23Na-41K atoms with tunable interspecies interactions and study the dynamics of coupled vortices in the different miscibility regimes. The BEC of sodium atoms obtained first in a Plug trap and later, in a crossed optical dipole trap, is fully characterized as well as the cold atomic cloud of potassium atoms produced by means of a Gray molasses cooling procedure. In the crossed optical dipole trap, the vortices will be nucleated with the use of a stirring beam. Therefore, in the end of this thesis, we present the stirring beam setup and its characterization prior aligning it into the 23Na BEC.
The field of ultracold matter has developed rapidly over the course of the past twenty to thirty years. One outstanding achievement has been the realisation of Bose-Einstein condensation (BEC) only 23 years ago. Many other fascinating observations of quantum phenomena have been made at an incredibly fast pace using ultracold atomic samples with contact force interactions as a testbed. Due to the rapid successes of all these experiments on atomic ensembles, researchers began to aim for more elaborate inter-particle interactions. A possible additional one is the dipole-dipole interaction (DDI), the long-range character of which stands out in comparison to the contact interactions. Moreover, DDI is anisotropic and the possibility to tune the direction of the dipoles in the experiment as well as the interaction strength promises the possibility to study a plethora of new quantum phenomena. In recent years, several experiments using different combinations of alkali atoms to create ground-state hetero-nuclear molecules in the ultracold regime have been set up, following the pioneering work on KRb molecules. Of all possible combinations of two alkali atoms, NaK combines the advantages of a high induced electric dipole moment of 2.72 Debye, chemical stability of the ground-state molecules, the possibility to realise bosonic as well as fermionic molecules and a large knowledge base for cooling and trapping of the two atomic species. This thesis reports on the development and construction of an experiment apparatus for the production of ultracold bosonic dipolar ground state 23Na39K molecules. This includes the setup of an ultra-high vacuum (UHV) system, several laser light sources, microwave (MW) and radio frequency (RF) antennas and electronics to control the various components of the experiment. The system pre-cools the atomic samples of 23Na and 39K and loads them into a dual-species three-dimensional magneto-optical trap (3D MOT). After a transfer to a magnetic quadrupole trap, the mixture is cooled by forced MW evaporation until three-body losses limit dual-species operation at high densities and zero magnetic field. Using the pure optical trapping potential of a crossed optical dipole trap (cODT) and RF- state-transfer, the scattering properties of the bosonic mixture of 23Na+39K are investigated in extensive atom loss measurements for a magnetic field range from 0 to 750 G. Several Feshbach resonances, zero crossings of the interspecies scattering length and inelastic loss features in many different scattering channels are identified. The results of this study are used to refine the molecular potentials of NaK and to produce a dual-species quantum-degenerate mixture of two BECs in the state (f = 1, mf = −1) of 23Na + (f = 1, mf = −1) of 39K. The measurements and refined molecular potentials will considerably aid in the future realisation of 23Na39K molecules in their absolute ground state.