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 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 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.
We report the production of 39K and 87Rb Bose–Einstein condensates (BECs) in the lowest hyperfine states | F = 1,mF = 1 〉 simultaneously. We collect atoms in bright/dark magneto-optical traps (MOTs) of 39K/87Rb to overcome the light-assisted losses of 39K atoms. Gray molasses cooling on the D1 line of the 39K is used to effectively increase the phase density, which improves the loading efficiency of 39K into the quadrupole magnetic trap. Simultaneously, the normal molasses is employed for 87Rb. After the microwave evaporation cooling on 87Rb in the optically plugged magnetic trap, the atoms mixture is transferred to a crossed optical dipole trap, where the collisional properties of the two species in different combinations of the hyperfine states are studied. The dual species BECs of 39K and 87Rb are obtained by further evaporative cooling in an optical dipole trap at a magnetic field of 372.6 G with the background repulsive interspecies scattering length a KRb = 34 a 0 (a 0 is the Bohr radius) and the intraspecies scattering length a K = 20.05a 0.
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.
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.
We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of 23Na and 39K. We prepare both optically trapped ensembles in the spin state $\left|f=1,{m}_{f}=\ensuremath{-}1\right\ensuremath{\rangle}$ and perform atom loss spectroscopy in a magnetic field range from 0 to 700G. The observed features include several s-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M}={m}_{\mathrm{Na}}+{m}_{\mathrm{K}}=\ensuremath{-}2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of 39K and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about 150G, which provides sizable intra- and interspecies scattering rates needed for fast thermalization. The impact of the differential gravitational sag on the miscibility criterion for the mixture is discussed. Our results serve as a promising starting point for the magnetoassociation into quantum degenerate 23Na39K Feshbach molecules.
We investigate quantum-mechanical interactions between ultracold rubidium and cesium in an optical trap at temperatures of a few microkelvin. Our results provide, on the one hand, an experimental key to understand the collisional properties and, on the other hand, a tool to control the interspecies interactions. By performing loss measurements we locate several Feshbach resonances, which provide insight into the energy structure of weakly bound RbCs molecules near the dissociation threshold and allow for the production of such heteronuclear Feshbach molecules. In the future we will transfer these loosely-bound molecules into the absolute internal ground state. The availability of ultracold heteronuclear ground state molecules will open the door to investigate phenomena associated with ultracold polar quantum gases. In our new experimental set-up we are able to trap and cool rubidium and cesium atoms in their lowest internal states. First we load both species into a two-color magneto-optical trap, having full control over the single-species atom number. We extend the technique of degenerate Raman-sideband cooling to a two-color version, which is able to simultaneously cool and polarize both rubidium and cesium. Thereafter we load the atoms into a levitated crossed optical dipole trap. Because of the presence of the gradient magnetic field the trap is highly state selective and consequently provides perfect spin-polarization of the sample. Furthermore, a coincidence of the magnetic-moment-to-mass ratios of the two species allows for simultaneous levitation of both, which assures an almost perfect spatial overlap between the species. We perform Feshbach spectroscopy in two different spin channels of the mixture within a magnetic field ranging from 20 to 300G. In the lowest spin combination of the species we locate 23 interspecies Feshbach resonances, while in a higher spin mixture we find 2 resonances. The high number of resonances found within this range of magnetic field is unusual for alkali mixtures. The presence of many resonances points to scattering properties of the mixture, which include higher-order coupling mechanisms. The obtained data on the Feshbach spectroscopy provide, on one hand, fundamental experimental input to characterize the Rb-Cs scattering properties and, on the other hand, identification of possible starting points for the association of ultracold heteronuclear RbCs molecules. In addition we show preliminary results on spectroscopy of the binding energy of RbCs dimers, based on a modulation of the magnetic field. The recently obtained Bose-Einstein condensate of Cs atoms, which represents a benchmark for the performance of the present apparatus, will be discussed as well as the potential pathways towards a double-degenerate mixture. We follow two main goals, first the production of a double Bose-Einstein condensate and, second, the transfer of shallow bound Feshbach molecules to the absolute internal ground state. The production of heteronuclear ground state molecules allows to enter the world of ultracold polar quantum systems.