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".
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".
An ultra-cold Fermi gas is a great way to simulate quantum many-body physics. The deeperunderstanding of strongly interacting fermionic systems gained from studying physics of such ultra-cold systems have found applications to high TC superconductors. The apparatus described here aims to study non-equilibrium dynamics and transport properties of unitary Fermi systems by optical cooling and trapping a cloud of 6Li atoms. My contribution to the design and construction of the Sommer group ultra-cold 6Li apparatus involves the design and construction of the Feshbach resonance electronics, AOM electronics for the laser system, setup of some of the AOM and ODT optics, and some coding. In this text I describe the design of our vacuum apparatus and laser system that traps and cools 6Li atoms to micro Kelvin temperatures, characterizes its performance, and describe how it can be utilized for spin transport experiments across normal-superfluid interface
We report our experimental apparatus for producing 6 Li quantum gases with good optical access. Atoms are first captured in a D 2 magneto-optical trap (MOT) and subsequently cooled via a compressed MOT and D 1 gray molasses, reaching sub-Doppler temperatures as low as 70 μ K . The cold atoms are then loaded into a single-beam optical dipole trap and transported into a compact octagonal glass cell, where forced evaporative cooling is performed. We achieve quantum degeneracy, observe the formation of a molecular Bose–Einstein condensate containing 1 × 10 5 atom pairs, and demonstrate controlled tomographic imaging, thereby establishing a versatile platform for future studies of three-dimensional (3D) superfluid dynamics.
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.
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.
An apparatus has been developed to create spin mixtures of ultracold fermionic 6Li in order to investigate the behavior of strongly interacting Fermi gases, and in particular, search for a superconducting phase transition. 6Li atoms are initially confined in a dual species magneto-optical trap (MOT) along with bosonic 7Li. Due to an overlap between spectral features of the two species, a D2/D1 trap/repump scheme is used for the 6Li. The atoms are subsequently cooled to quantum degeneracy in a magnetic trap through optimized dual forced evaporation and transferred to an all optical trap where spin mixtures are created with RF sweeps and pulses. The atomic interactions are controlled through the use of magnetic Feshbach resonances and an externally applied bias magnetic field of up to 1000 G. This thesis details the construction, operation, and performance of the 6Li portion of the apparatus, as well as current results.
Laser cooling and atom trapping techniques have enabled atomic physicists to attain temperatures on the order of 100 nK. In this regime, a trapped gas must be described within the framework of quantum statistical mechanics. In 1995, Bose-Einstein condensation (BEC) was achieved for the first time in such a system by three independent groups. The success of attaining BEC has encouraged research in quantum degenerate Fermi gases (DFG). One of the most exciting opportunities for a DFG is the prospect for Cooper pairing in a two-component gas. The experimental techniques for obtaining degenerate gases, as well as the mechanism for Cooper pairing, hinges on understanding and characterizing ultracold collisional interactions.\nThis thesis is a twofold study in this exciting field. The first section is an in-depth treatment of collisions in atomic lithium. Lithium has two isotopes, 6Li which is a fermion and 7Li which is a boson. This makes it an ideal candidate for studying quantum degenerate gases. In a series of experiments using a magneto-optical trap, we have spectroscopically measured the ground and excited state molecular potentials for both isotopes. From this work we have been able to obtain the most accurate potentials for lithium to date. These precise measurements have enabled us to extract the most accurate value to date for the 2P atomic radiative lifetime of lithium. Furthermore, we have developed a coupled-channel treatment of two-body collisions which has enabled us to calculate the scattering amplitude, elastic cross section, and rate of spin-exchange decay for any ground state collision in lithium as a function of temperature and magnetic field.\nArmed with this knowledge, we have made progress on the design and construction of an electromagnetic trap for lithium. This trap will enable the study of a degenerate Fermi gas of 6Li as well as the possibility of observing a Cooper pairing transition. The trap performance has been characterized for each isotope and current work is focussed on cooling lithium down to degeneracy. Measurements of spin-exchange decay have been made and compare well with the collisional theory that has been developed.