An apparatus for producing atomic-gas Bose-Einstein condensates (BECs) of 87-Rb atoms is described. The apparatus produces 87-Rb BECs in a dual-chamber vacuum system that incorporates magnetic transport of trapped atoms from the magneto-optical trapping cell to the BEC production cell via the operation of a series of overlapping magnet coils. The design, construction, and operation of the apparatus are described in detail. The apparatus is used to study the creation of quantized vortices in BECs by the merging and interference of multiple trapped condensates. In this experiment, a single harmonic potential well is partitioned into three sections by an optical barrier, enabling the simultaneous formation of three independent, uncorrelated BECs. The BECs may either merge together during their growth, or, for high-energy barriers, the BECs can be merged together by barrier removal after their formation. Either process may instigate vortex formation in the resulting BEC, depending on the initially indeterminate relative phases of the condensates and the merging rate.
An apparatus for producing atomic-gas Bose-Einstein condensates (BECs) of 87-Rb atoms is described. The apparatus produces 87-Rb BECs in a dual-chamber vacuum system that incorporates magnetic transport of trapped atoms from the magneto-optical trapping cell to the BEC production cell via the operation of a series of overlapping magnet coils. The design, construction, and operation of the apparatus are described in detail. The apparatus is used to study the creation of quantized vortices in BECs by the merging and interference of multiple trapped condensates. In this experiment, a single harmonic potential well is partitioned into three sections by an optical barrier, enabling the simultaneous formation of three independent, uncorrelated BECs. The BECs may either merge together during their growth, or, for high-energy barriers, the BECs can be merged together by barrier removal after their formation. Either process may instigate vortex formation in the resulting BEC, depending on the initially indeterminate relative phases of the condensates and the merging rate.
We report observations of vortex formation by merging and interfering multiple (87)Rb Bose-Einstein condensates (BECs) in a confining potential. In this experiment, a single harmonic potential well is partitioned into three sections by a barrier, enabling the simultaneous formation of three independent, uncorrelated BECs. The BECs may either automatically merge together during their growth, or for high-energy barriers, the BECs can be merged together by barrier removal after their formation. Either process may instigate vortex formation in the resulting BEC, depending on the initially indeterminate relative phases of the condensates and the merging rate.
We study the formation of vortices in a Bose-Einstein condensate (BEC) that has been prepared by allowing isolated and independent condensed fragments to merge together. We focus on the experimental setup of Scherer et al. [Phys. Rev. Lett. 98, 110402 (2007)], where three BECs are created in a magnetic trap that is segmented into three regions by a repulsive optical potential; the BECs merge together as the optical potential is removed. First, we study the two-dimensional case; in particular, we examine the effects of the relative phases of the different fragments and the removal rate of the optical potential on the vortex formation. We find that many vortices are created by instant removal of the optical potential regardless of relative phases, and that fewer vortices are created if the intensity of the optical potential is gradually ramped down and the condensed fragments gradually merge. In all cases, self-annihilation of vortices of opposite charge is observed. We also find that for sufficiently long barrier ramp times, the initial relative phases between the fragments leave a clear imprint on the resulting topological configuration. Finally, we study the three-dimensional system and the formation of vortex lines and vortex rings due to the merger of the BEC fragments; our results illustrate how the relevant vorticity is manifested for appropriate phase differences, as well as how it may be masked by the planar projections observed experimentally.
The presence of quantized vortices and a high level of control over trap geometries and other system parameters make dilute-gas Bose-Einstein condensates (BECs) a natural environment for studies of vortex dynamics and quantum turbulence in superfluids, primary interests of the BEC group at the University of Arizona. Such research may lead to deeper understanding of the nature of quantum fluid dynamics and far-from-equilbrium phenomena.Despite the importance of quantized vortex dynamics in the fields of superfluidity, superconductivity and quantum turbulence, direct imaging of vortices in trapped BECs remains a significant technical challenge. This is primarily due to the small size of the vortex core in a trapped gas, which is typically a few hundred nanometers in diameter. In this dissertation I present the design and construction of a new ^87Rb BEC apparatus with the goal of studying vortex dynamics in trapped BECs. The heart of the apparatus is a compact vacuum chamber with a custom, all-glass science cell designed to accommodate the use of commercial high-numerical-aperture microscope objectives for in situ imaging of vortices.The designs for the new system are, in part, based on prior work in our group on in situ imaging of vortices. Here I review aspects of our prior work and discuss some of the successes and limitations that are relevant to the new apparatus. The bulk of the thesis is used to described the major subsystems of the new apparatus which include the vacuum chamber, the laser systems, the magnetic transfer system and the final magnetic trap for the atoms. Finally, I demonstrate the creation of a BEC of ~2x10^6 ^87Rb atoms in our new system and show that the BEC can be transferred into a weak, spherical, magnetic trap with a well defined magnetic field axis that may be useful for future vortex imaging studies.
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.
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.
We describe a versatile and simple scheme for producing magnetically and optically trapped 87 Rb Bose–Einstein condensates, based on a moving-coil transporter apparatus. The apparatus features a TOP trap that incorporates the movable quadrupole coils used for magneto-optical trapping and long-distance magnetic transport of atomic clouds. As a stand-alone device, this trap allows for the stable production of condensates containing up to one million atoms. In combination with an optical dipole trap, the TOP trap acts as a funnel for efficient loading, after which the quadrupole coils can be retracted, thereby maximizing optical access. The robustness of this scheme is illustrated by realizing the superfluid-to-Mott insulator transition in a three-dimensional optical lattice.