Theses

Design, construction, and performance towards a versatile 87Rb and 41K BEC apparatus -- MPhil, N. McKay Parry (2016)
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.

Design, construction & characterisation of a versatile high atom number BEC apparatus -- Honours, T. A. Bell (2014)
Bose Einstein Condensates represent a valuable experimental medium for the study and application of fundamental atomic science. Within tailored trapping potentials, many exotic quantum phenomena may be probed or exploited, including Feshbach resonances, atomic clock measurements, Bragg spectroscopy, and superfluidity. While experimental condensates were first produced within magnetic traps, optical potentials are advantageous for interferometry, since they permit spin entangled sensitivity enhancement. Exploit- ing the strengths of each distinct approach, hybrid methods were proposed for the rapid production of large condensates within optical potentials. Following the work of, the present thesis aims to experimentally develop an optimised hybrid apparatus for the rapid production of condensates within optical potentials. Although condensates have not yet been produced, many preliminary trapping configurations have been demonstrated, representing substantial progress for the year available. We have successfully generated large Magneto- Optical Traps with 3 × 109 atoms, and Compressed Magneto-Optical Traps of 1.2 × 109 at temperatures of 32μK. Long lived Magnetic Traps with up to 3 × 108 atoms have been ad- ditionally formed. Transfer into the magnetic potential is however not yet optimised, with larger numbers expected once magnetic bias fields are employed to spatially overlap trap centres. Implementing a period of optical pumping should also increase loading into the magnetic potential. To form condensates it remains to firstly compress and evaporatively cool within the magnetic potential. An Optical Dipole Trap must then be overlapped and evaporative cooling continued to degeneracy.

All-optical 87Rb Bose-Einstein condensate apparatus: construction and operation -- PhD, I. L. H. Humbert (2012)
A new apparatus was built by the author and we report on the experimental details of the trapping of 87Rb atoms from a hot vapour and cooling them in a magneto-optical trap, and further evaporation to quantum degeneracy in a crossed optical dipole trap operating at a wavelength of λ = 1064nm, with accurate control of the power in both beams via a feedback loop. The evaporation of neutral atoms of 87Rb in far red detuned optical dipole traps using linearly polarised laser light is spin independent, and mixed spinor condensates of the F=1 manifold can be formed. As an empirical technique we found by applying a magnetic gradient field during the final evaporation that we can selectively populate mF spin states or prepare mixtures. This intriguing mechanism was found earlier as well by M. S. Chang, but is yet not fully understood and subject of our future research. We can now routinely prepare an almost pure condensate containing up to 7000 atoms in the condensed phase purely in the mF = 0 spin state.

Bose-Einstein Condensates in Non-Harmonic Optical Potentials -- PhD, Sebastian Schnelle (2011)
This thesis presents work on Bose-Einstein condensates in non-harmonic optical potentials. First, a new trap design developed at the University of Queensland is presented that allows the creation of nearly arbitrary two-dimensional potential landscapes by spatially scanning a far red-detuned laser beam using a two-dimensional acousto-optic modulator. In conjunction with a feed-forward technique this trap is capable of producing optical traps which have the necessary stability to be used in ultra-cold atom research. Different geometries are presented. In particular toroidal trap geometries are discussed which are interesting because they offer the possibility for a multiply connected Bose-Einstein condensate. The trap also offers the possibility of dynamic potentials which have been employed to measure the critical velocity of superfluidity in Bose-Einstein condensates. Secondly, measurements on condensation dynamics are presented which use an optical dim- ple potential superimposed upon a harmonic magnetic trap. In the experiments the dimple potential is ramped on slowly or turned on suddenly for a range of dimple depths and widths and the condensate fraction and temperature are measured as a function of hold times. Lastly, progress on experiments to measure the critical velocity of superfluidity in Bose- Einstein condensates is reported.