We report on the design and construction of a versatile setup for experiments with ultracold lithium (Li) gases. We discuss our methods to prepare an atomic beam and laser cool it in a Zeeman slower and a subsequent magneto-optical trap, which rely on established methods. We focus on our laser system based on a stable interference-filter-stabilized, linear-extended-cavity diode laser, so far unreported for lithium wavelengths. Moreover, we describe our optical setup to combine various laser frequencies for cooling, manipulation, and detection of Li atoms. We characterize the performance of our system preparing degenerate samples of Li atoms via forced evaporation in a hybrid crossed-beam optical-dipole trap plus confining magnetic trap. Our apparatus allows one to produce quantum gases of N ≈ 105…106 fermionic lithium-6 atoms at nanokelvin temperatures in cycle times below 10 s. Our optical system is particularly suited to study the dynamics of fermionic superfluids in engineered optical potentials.
Ultracold mixture experiments hold the promise of providing new insights into many-body quantum systems as well as ultracold chemistry and few-body phenomena. The work presented in this thesis dealt with the construction of a new apparatus for the production and study of ultracold gases of fermionic lithium-6 and bosonic caesium-133. These isotopes offer a wide tunability in their interaction strength, both in inter-species and intra-species collisions, through magnetic Feshbach resonances. Additionally, the widely different resonance frequencies of lithium and caesium enables independent control of each of the species. With this apparatus, Bose-Einstein condensates (BEC) containing 10^4 lithium Feshbach molecules are routinely produced. The cooling system for caesium has been developed in parallel and important steps towards producing ultracold caesium gases have been made. An optical dipole trap has been loaded with 2x10^6 caesium atoms and evaporative cooling towards quantum degeneracy can now be pursued. Laser, vacuum, magnetic and control systems have been developed for the implementation of this experiment. Light produced with this laser system was used to laser cool atoms, create conservative dipole traps as well as to provide means of imaging atomic clouds. Additionally, a system to produce strong magnetic fields of up to 1400 G has been established in order to exploit the wide tunability in the atomic interactions. Software that was developed for the computerised control system facilitated the coordination of all the components involved in the experimental sequence. Measurements and calculations that showcase the functionality of relevant parts of the setup are presented in this thesis. In this experiment, lithium and caesium atoms are obtained from a novel type of Zeeman slower and are loaded into a magneto-optical trap (MOT). The system is capable of doing this independently for each of the atomic species as well as sequentially. After the MOT has been loaded with atoms, they are transferred into a conservative far-off-resonance optical dipole trap. By adjusting the interactions between atoms and lowering the depth of the dipole trap, efficient evaporative cooling of lithium was carried out from which a molecular BEC was obtained. Time-of-flight measurements were used to characterise the condensate and study its expansion dynamics.
This thesis presents novel techniques for the experimental study of ultracold quantum gases of fermionic lithium and potassium atoms.In the first part of this thesis, we describe the design and characterization of the new components of our experimental apparatus capable of trapping and cooling simultaneously
6Li and
40K atoms to ultracold temperatures.We report on a novel sub-Doppler cooling mechanism, operating on the D
1 line transition of alkali atoms, for laser cooling of lithium and potassium. The measured phase space densities after this molasses phase are on the order of
10−4 for both
6Li and
40K. We present the forced evaporative cooling of
40K atoms, starting in an optically plugged magnetic quadrupole trap and continuing in an optical dipole trap. In this context, we report on the production of a quantum degenerate Fermi gas of
1.5×105 atoms
40K in a crossed dipole trap with
T/TF=0.17, paving the way for the study of strongly interacting superfluids of
40K.In the second part of this thesis, we present a narrow-linewidth, all-solid-state laser source, emitting 5.2 W in the vicinity of the lithium D-line transitions at 671 nm. The source is based on a diode-end-pumped unidirectional ring laser operating on the 1342 nm transition of Nd:YVO
4, capable of producing 6.5 W of single-mode light delivered in a diffraction-limited beam. We report on three different approaches for second-haromonic generation of its output beam, namely by employing an enhancement cavity containing a ppKTP crystal, intracavity frequency doubling and a ppZnO:LN waveguide structure.
Ultracold gases provide a clean setup for investigating the many-body physics of stronglyinteracting fermions. Due to the universal nature of strongly interacting fermionic systems, an ultracold gas can serve as a quantum simulator for other strongly interacting systems of fermions such as neutron stars and high-Tc superconductors [1] [2]. A better understanding of such systems could potentially have great scientific and technological implications. In this thesis, I describe the construction of an apparatus that can be used for future experiments on ultracold atoms probing questions related to spin and heat transport in a strongly interacting gas of 6Li atoms. Multiple stages of cooling have been successfully completed on the way towards establishing a quantum degenerate ultracold gas of Li-6. To this end a magneto-optical trap (MOT) has been realized with a temperature on the order of ? 1mK, a compressed MOT (cMOT) has been realized with a temperature ? 600?K, and most recently a crossed optical-dipole trap (ODT) with a temperature ? 70?K. The foundations have also been laid for the final stage of atomic trapping in our apparatus, the multi-region trap, or "box trap"; in particular I will describe an optical setup that has been tested and is suitable for use in creating the hollow cylindrical walls or our box trap, which we like to call the "ring beam".
We describe our experimental apparatus for generating quantum degenerate gases of bosonic 174Yb and fermionic 173Yb atoms. We use a Zeeman slower to generate a slow atomic beam and collect atoms in a magneto-optical trap formed by 556-nm laser beams without frequency modulations. Laser-cooled ytterbium atoms are transferred to a crossed optical dipole trap and evaporatively cooled to quantum degeneracy. Our system generates a Bose-Einstein condensate containing over 6 × 104 174Yb atoms or a degenerate Fermi gas of about 7 × 104 173Yb atoms at T/T F =0.8(1), where T F is the Fermi temperature of the gas. We highlight the high performance of the Zeeman slower and the home-made frequency-doubling systems for 399-nm and 556-nm lasers.
Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".