The aim of our experiment is to explore two methods of creating an ultracold dipolar gas which can subsequently be used to simulate quantum phenomena. The first method is to sympathetically cool polar molecules. In this case, the molecules are overlapped with ultracold lithium atoms, thus allowing the two clouds to thermalise through elastic collisions. The second method is to electrically polarise ultracold lithium atoms using an electric field of approximately 1MV/cm. This involves placing the atoms between two high voltage electrodes. This thesis describes and characterises the setup used to produce, trap and transport a cloud of lithium-7 atoms. The setup consists of a lithium oven, Zeeman slower, magneto-optical trap (MOT) and magnetic trap. Up to 2.3×10^8 atoms are loaded into the MOT with an initial temperature of 1.3 mK. By implementing a compressed MOT phase the temperature is reduced to 0.75 mK. Before transport, 23% of the MOT atoms are transferred into the magnetic trap, which has a lifetime of 1.53±0.01 s in the MOT chamber. Using a motorised translation stage to move the magnetic trapping coils, atomic transport over a distance of 44 cm from the MOT chamber to the science chamber has been demonstrated. The transport efficiency is 41%. In the science chamber the lifetime of the magnetic trap has been measured as 18.5±0.7 s. Experiments to optimise the absorption imaging system have also been carried out, highlighting the fact that a time and position dependent magnetic field is present after the trapping coils switch off. The feasibility of producing a 1MV/cm electric field has been investigated. By using indium tin oxide coated glass electrodes in an adjustable electrode mount, an electric field of approximately 0.2MV/cm has been generated. These electrodes were subsequently replaced with super-polished stainless steel electrodes which generated a field of 0.38MV/cm.
The aim of our experiment is to explore two methods of creating an ultracold dipolar gas which can subsequently be used to simulate quantum phenomena. The first method is to sympathetically cool polar molecules. In this case, the molecules are overlapped with ultracold lithium atoms, thus allowing the two clouds to thermalise through elastic collisions. The second method is to electrically polarise ultracold lithium atoms using an electric field of approximately 1MV/cm. This involves placing the atoms between two high voltage electrodes. This thesis describes and characterises the setup used to produce, trap and transport a cloud of lithium-7 atoms. The setup consists of a lithium oven, Zeeman slower, magneto-optical trap (MOT) and magnetic trap. Up to 2.3×10^8 atoms are loaded into the MOT with an initial temperature of 1.3 mK. By implementing a compressed MOT phase the temperature is reduced to 0.75 mK. Before transport, 23% of the MOT atoms are transferred into the magnetic trap, which has a lifetime of 1.53±0.01 s in the MOT chamber. Using a motorised translation stage to move the magnetic trapping coils, atomic transport over a distance of 44 cm from the MOT chamber to the science chamber has been demonstrated. The transport efficiency is 41%. In the science chamber the lifetime of the magnetic trap has been measured as 18.5±0.7 s. Experiments to optimise the absorption imaging system have also been carried out, highlighting the fact that a time and position dependent magnetic field is present after the trapping coils switch off. The feasibility of producing a 1MV/cm electric field has been investigated. By using indium tin oxide coated glass electrodes in an adjustable electrode mount, an electric field of approximately 0.2MV/cm has been generated. These electrodes were subsequently replaced with super-polished stainless steel electrodes which generated a field of 0.38MV/cm.
Trapping particles is a key starting point for a range of physics experiments. The ability to confine, manipulate and interrogate a trapped species enables an invaluable degree of control and precision. Each trap offers different advantages and possibilities, and emerging experiments often demand different methods of trapping. This thesis describes a new three-dimensional microwave trap for atoms and molecules. Like an optical dipole trap, it can trap ground state polar molecules, but its depth and volume are larger by factors of 10^3 and 10^9 respectively. The experiment consists of a lithium oven, Zeeman slower, magneto-optical trap (MOT), a moving magnetic trap, and a high-quality Fabry-Perot cavity which serves as the microwave trap. Starting from a MOT of 1×10^8 lithium-7 atoms, the atomic cloud is cooled from a temperature of around 1mK to 41(1)μK with the recently developed Raman grey molasses method. Next, the population is optically pumped to a magnetically trappable state, and up to 85(2)% are loaded into a quadrupole magnetic trap. These atoms are then transferred to a moving magnetic trap and translated 600mm to the centre of the microwave cavity. After optimizing the transport to minimize atom heating and loss, we can produce samples of 2×10^7 atoms in the microwave chamber, at a phase space density of 3.58(15)×10^7. Finally, loading of the microwave trap is demonstrated and its basic properties studied. When the input power to the cavity is 610W, the electric field amplitude at the centre reaches roughly 20kV/cm. At this input power, centre-of-mass oscillation frequencies in the microwave trap were measured as 28.55(5)Hz along the axis of the cavity, and 8.81(8)Hz along the orthogonal direction. The observed lifetime was 1.76(12)s, limited by the vacuum quality. The atomic cloud expands and cools to 22(3)μK when loaded into the microwave trap, with a phase space density of 4(1)×10^7. This is consistent with adiabatic loading from the magnetic trap.
Arrays of cold atoms in magnetic traps have been implemented for use in quantum simulation, metrology, and ultracold chemistry. The scope of all of these fields could be greatly enhanced with cold and ultracold molecules. Cooling and trapping molecules, however, poses unique challenges compared to atoms. Sympathetic cooling, whereby molecules are cooled via collisions with ultracold atoms, will be a key technique for achieving the required densities and temperatures.\\ Towards this end, the Carty group in Durham has constructed a moving-trap Zeeman decelerator (`MTZD'), based on the same operating principles as a conventional Zeeman decelerator but producing a truly dynamic three-dimensional trapping potential. We have begun to characterise the decelerator with metastable argon, showing 3D guiding and deceleration, and intend to move to molecules in the near future.\\ In the longer term the decelerator is intended to load a magnetic trap. Presented here are the findings from preliminary work to design a hybrid magnetic trap with magneto-optical trap capability, or `MT-MOT'. The MT-MOT comprises six toroidal permanent magnets plus switchable electromagnetic coils. We have performed simulations to determine the feasibility of co-loading lithium atoms and calcium hydride molecules. Some consideration of loss mechanisms and likely trap lifetimes are discussed.
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 describes the design, construction and optimisation of a new apparatus to produce Bose-Einstein condensates (BECs) of 87Rb atoms. The main aim in building this system was to include a high resolution imaging system capable of resolving single atoms. Optical access for the imaging system was created by including a stage of atom transport in which the atoms are magnetically transferred ~50 cm from a magneto-optical trap (MOT), where they are initially collected, to a glass science cell where experiments are carried out and imaging takes place. Two magnetic transport schemes have been demonstrated, based on approaches first used in other laboratories. First, a scheme in which the atoms are transferred in a moving pair of magnetic trapping coils. Second, a hybrid scheme where the atoms are translated part of the distance in the moving coils, and the rest of the way by switching the current in a chain of fixed coils. This second scheme was designed to allow optical access for a high numerical aperture microscope objective to be placed immediately next to the science cell for high resolution imaging.The atoms were first collected in a large pyramid MOT which can be loaded with 3 × 10^9 atoms in a time of 20 s. Around half of these atoms – those in the |F = 1, mF = −1> magnetic substate – were then magnetically trapped prior to transport. The typical fraction of the trapped atoms transferred to the science cell was ~30% and ~18% for the moving coils and hybrid schemes respectively.Evaporative cooling was carried out on the atom cloud following transport with the moving coils and loading into a time-orbiting potential trap. The optimised cooling sequence lasted for 28 s and consistently produced a pure condensate with 5 × 10^5 atoms. A BEC has also been produced by evaporative cooling following hybrid transport. The next experimental steps will be to optimise the hybrid transfer approach further and install the high resolution imaging system.The system is well-placed to continue an ongoing series of experiments in which ultracold atoms are trapped in RF-dressed potentials. These potentials will be used to study low-dimensional quantum gases as well as in experiments where small atom number BECs are rapidly rotated to enter the fractional quantum Hall regime.
This thesis describes a new apparatus designed to study ultracold gases of rubidium. The apparatus comprises a six-beam MOT chamber and a dierential pumping stage leading into a 'science chamber'. This science chamber is constructed from a rectangular glass cell. Atomic gases of rubidium are collected in a MOT and then transferred into a magnetic quadrupole trap. This quadrupole trap is mounted on a motorised translation stage. This setup transports the atoms into the science chamber, where they are transferred into a static quadrupole trap which is built around the glass cell. During the transport the atoms are deected over a glass prism, which shields the science chamber from stray rubidium from the MOT chamber. The magnetic transport is studied in detail and the deection over the glass prism is fully described simulating the displacement of the quadrupole trap. Using the magnetic quadrupole trap in the science chamber to store one rubidium isotope, we are able to load the other rubidium isotope in the MOT chamber and transfer it also into the science chamber. There, the two magnetic traps are merged and variable ratios of isotopic mixtures can be created. The merging of the two quadrupole traps could be employed in future experiments to cool 85Rb sympathetically with 87Rb. In the science chamber forced radio-frequency evaporation is performed and the loading of a far-detuned dipole trap is studied. Initially the dipole trap is realised as a hybrid trap, a single beam dipole trap in combination with the quadrupole trap. Further studies include the loading of a crossed beam dipole trap. We demonstrate that the apparatus is capable of producing 87Rb condensates. Preliminary studies of 85Rb in the dipole trap are included which hopefully in future will lead to a quantum degenerate gas of 85Rb.
Integrating two chemically distinct atomic species into a miniaturized, high-flux cold-atom source is a key challenge for modern experiments with ultracold atomic mixtures and polar molecules. Here, we report a compact setup with in-series two-dimensional magneto-optical traps (2D MOTs) that provides high-flux cold lithium and rubidium atoms. Thanks to the efficient short-distance Zeeman slowing, the maximum 3D MOT loading rate of lithium atoms reaches a record value of 6.6 × 10 9 atoms/s at a moderate lithium-oven temperature of 372 degrees Celsius, which is 44 times higher than that without the Zeeman slowing light. The flux of rubidium is also as high as 2.3 × 10 9 atoms/s with the rubidium oven held at room temperature. Meanwhile, the entire vacuum-chamber system, including an ultra-high-vacuum science cell, is within a small volume of 65 × 55 × 70 cm 3 . Our work represents a substantial improvement over traditional bulky and complex dual-species cold-atom setups. It provides a good starting point for the fast production of a double-degenerate lithium-rubidium atomic mixture and large samples of ultracold lithium-rubidium ground-state molecules.