1) species show a preference for the MJ = ±1 sub-levels. For these bands the electronic alignment is very similar to that observed in the dissociation of OCS, indicating a similar mechanism, at least in the exit channel, is responsible for the polarisation in both systems.

No description available.

Typescript (Photocopy) / Bibliography: leaves vii-xiv. (second sequence) / [viii], 192, [34], xiv leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1989

Various aspects of three-dimensional spin foam models for quantum gravity are discussed. Spin foam models and graphical calculus are introduced via the Ponzano-Regge model for 3d gravity and some important properties of this model are described. The asymptotic formula for the 6j symbol found by Ponzano and Regge is generalised to include the Ponzano-Regge amplitude for triangulations of handlebodies. Some simple observables are computed in a model for fermions coupled to 3d gravity. The result is a sum over spin foam models with certain vertex amplitudes which are described. An explicit example is given and the vertex amplitudes expressed in terms of 6j symbols. Finally, a group field theory for this spin foam model is described.

The growing fields of spintronics and nanotechnology have created increased interest in developing the means to manipulate the spin of electrons. One such method arises from the combination of the spin-orbit interaction and the broken inversion symmetry that arises at surfaces and interfaces, and has prompted many recent investigations on metallic surfaces. A method by which surface states, in the absence of spin orbit effects, have been successfully investigated is the Green function embedding scheme of Inglesfield. This has been integrated into a self consistent FLAPW density functional framework based on the scalar relativistic K¨olling Harmon equation. Since the spin of the electron is a direct effect of special relativity, calculations involving the spin orbit interaction are best performed using solutions of the Dirac equation. This work describes the extension of Green’s function embedding to include the Dirac equation and how fully relativistic FLAPW surface electronic structure calculations are implemented. The general procedure used in performing a surface calculation in the scalar relativistic case is closely followed. A bulk transfer matrix is defined and used to generate the complex band structure and an embedding potential. This embedding potential is then used to produce a self consistent surface potential, leading to a Green’s function from which surface state dispersions and splittings are calculated. The bulk embedding potential can also be employed in defining channel functions and these provide a natural framework in which to explore transport properties. A relativistic version of a well known expression for the ballistic conductance across a device is derived in this context. Differences between the relativistic and nonrelativistic methods are discussed in detail. To test the validity of the scheme, a fully relativistic calculation of the extensively studied spin orbit split L-gap surface state on Au(111) is performed, which agrees well with experiment and previous calculations. Contributions to the splitting from different angular momentum channels are also provided. The main advantages of the relativistic embedding method are the full inclusion of the spin orbit interaction to all orders, the true semi infinite nature of the technique, allowing the full complex bands of the bulk crystal to be represented and the fact that a only small number of surface layers is needed in comparison to other existing methods.

In this thesis I describe experimental work and present data on the guiding of Rubidium atoms along free-space propagating light beams as well as within hollow core glass fibres, namely photonic crystal fibres. I describe experiments, laser systems and vacuum trap assemblies designed to facilitate this guiding. These experiments are intended to aid progression within the field of cold atom guidance wherein narrow diameter, long distance hollow-fibre guides are a current goal. Realisation of these guides could lead to promising applications such as atom interferometers and spatially accurate, multi-source, atom depositors. Herein, guided fluxes are observed in free-space guiding experiments for distances up to 50mm and up to 10GHz red-detuning from resonance. Additionally hollow-core, Kagome structured, quasi- and true-photonic crystal fibres are characterised. Finally a number of detailed fibre-guiding magneto-optic traps are developed. Both cold atomic-beams and cold atomic clouds are reliably positioned above fibre entrance facets in conjunction with a guiding laser beam coupled into the fibre core. Issues regarding optical flux detection outwith fibre confinement appear to have hindered observation of guided atoms. A far more sensitive detection system has been developed for use in current, ongoing fibre-guide experiments.

This thesis explores the theoretical foundations of cross-phase modulation (XPM) between optical fields in the N-configuration atom. This is the process by which the refractive index experienced by one field can be modulated by controlling the intensity of another. The electro-optical version of this effect was first discovered by John Kerr in 1875 and found applications in photonics as a means of very rapidly modulating the phase and intensity of electromagnetic fields. Due to recent advances in experimental techniques there has been growing interest in generating nonlinear optical interactions in coherently prepared atomic ensembles. The use of coherently prepared media brings the possibility of achieving a much larger cross-phase modulation than is possible using classical materials. This is particularly useful when trying to create large optical nonlinearities between low-intensity electromagnetic fields. Much of the current research into cross-phase modulation is directed towards realising potential applications in the emerging field of quantum information processing. Above all, the possibility of constructing an all-optical quantum computer has been at the heart of much research and controversy in the field. In this thesis the theory of steady-state, transient and pulsed cross-phase modulation is developed. Moreover, care has been taken to relate all research back to experimentally feasible situations. As such, the relevance of the theory is justified by consideration of the situation present in rubidium-87. Due to the close relationship between XPM in the N-configuration atom and electromagnetically induced transparency in the Lambda-atom, many similarities and insights act as link between these two fields. Indeed, it is frequently demonstrated that the key to understanding the various properties of XPM in the N-configuration atom is by comparison with the situation in the corresponding Lambda-atom equivalent.

Understanding the structure of matter in the solid state could be considered as being one of ‘the big questions’ in chemistry. Whereas the structural behaviour of molecules in the gas phase is relatively well-understood, this is not the case for the condensed phase due to the complexity of short and long-range intermolecular interactions. The purpose of the work in this thesis is to examine the structural response of solid molecular materials to stimuli of extreme pressure and temperature. L-alanine crystallises as a zwitterion in the space group P212121. Neutron powder diffraction and X-ray single crystal diffraction data show that the a and caxes are very similar in length. The a-axis is more compressible than the c-axis, and at ca. 2 GPa the cell becomes metrically tetragonal, however the underlying symmetry is still orthorhombic. The structure remains in a compressed form of the ambient phase up to 9.87 GPa. Previous Raman and energy dispersive powder diffraction studies have interpreted changes in spectra at ca. 2 and 9 GPa as phase transitions. The diffraction data and DFT calculations described here suggest that these are in fact due to changes in conformation of the ammonium group. L-alanine shows remarkable resistance to the effects of pressure but something must happen to the structure if pressure continues to be increased. Neutron powder diffraction has been used to obtain high-pressure data for L-alanine up to 15.46 GPa. These are the highest-pressure diffraction data reported for any amino acid. Above ca. 15 GPa, L-alanine undergoes a reversible transition to an amorphous phase through volume collapse of the crystal, driven by the need to minimise the PV term in the Gibbs free energy equation, as opposed to relieving destabilising contacts. It is currently the only amino acid known to undergo a transition of this type. The co-crystal of methylpyridine and pentachlorophenol (MP-PCP) forms in the space group P-1. When the phenolic proton is deuterated (MP-PCP-d) it exhibits isotopic polymorphism, crystallising in the space group Cc. Structures of the two other combinations of isotope and space group, i.e MP-PCP in Cc and MP-PCP-d in P-1 have not yet been determined. We demonstrate that these polymorphs can be obtained using high-pressure and low-temperature conditions predicted by thermodynamics. The use of in-situ crystallisation at pressure has driven MP-PCP to pack with Cc symmetry, minimising the PV term in the Gibbs free energy equation. Low-temperature crystallisation causes MP-PCP-d to form in P-1 due to this phase being favoured by vibrational enthalpic and entropic contributions. Aniline is a liquid under ambient conditions but freezes at 267 K in the monoclinic space group P21/c. It can also be frozen by pressure (ca. 0.8 GPa) in the orthorhombic space group Pna21. Neutron powder diffraction shows that on decompression the orthorhombic form transforms to the monoclinic phase at 0.3 GPa, owing to the monoclinic packing being less dense. PIXEL calculations provide an insight into the intermolecular energies of the orthorhombic crystal up to 7.301 GPa. They show that dispersive forces are more dominant than the hydrogen bonds, one of which becomes destabilising at higher pressure. Thermodynamic calculations estimating the relative stabilities of the two polymorphs prove inconclusive owing to improper treatment of dispersion interactions by Density Functional Theory calculations. The structural behaviour of cyclohexane in the crystalline (P21/c) and plastic phases (Fm3m) has been studied using neutron total scattering data and Reverse Monte Carlo (RMC) modelling. Atomistic models show that the molecules exhibit correlated motion as they prepare to undergo transformation on heating. Inclusion of I(t) data in the RMC refinements is shown to be important as when it is not accounted for, the RMC method is incapable of distinguishing the form of the disorder in the plastic phase. Molecular motion in this phase is shown to be correlated through the avoidance of short intermolecular D···D contacts. The ordered and disordered solid phases of oxalyl chloride (space groups P21/c and Pbca respectively) have been studied by neutron total scattering and modelled using a Reverse Monte Carlo approach. Atomistic models show that on heating, the atoms vibrate out of the plane of the molecule until 245 K where they show approximately isotropic vibration owing to reduced steric restriction. This may provide the molecules with the freedom they require to rotate and undergo the solidsolid transition. The onset of disorder has also been partially predicted by molecular dynamics simulations. RMC modelling does not provide satisfactory atomic configurations of the disordered solid phase due to an unrealistic distribution of intermolecular chlorine-chlorine contacts. This study presents an example of a flexible, 3-atom-type system that may be too complex for analysis by the RMC method.

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.

Ultracold atoms in optical lattices can be used to model condensed matter systems. They provide a clean, tuneable system which can be engineered to reach parameter regimes that are not accessible in condensed matter systems. Furthermore, they provide different techniques for probing the properties of these systems. This thesis presents an experimental and theoretical study of ultracold atoms in optical lattices for quantum simulation of two-dimensional systems.The first part of this thesis describes an experiment with a Bose-Einstein condensate of 87Rb loaded into a two-dimensional optical lattice. The beams that generate the optical lattice are controlled by acousto-optic deflection to provide a flexible optical lattice potential. The use of a dynamic ‘accordion’ lattice with ultracold atoms, where the spacing of the lattice is increased in both directions from 2.2 to 5.5 μm, is described. This technique allows an experiment such as quantum simulations to be performed with a lattice spacing smaller than the resolution limit of the imaging system, while allowing imaging of the atoms at individual lattice sites by subsequent expansion of the optical lattice. The optical lattice can also be rotated, generating an artificial magnetic field. Previous experiments with the rotating optical lattice are summarised, and steps to reaching the strongly correlated regime are discussed. The second part of this thesis details numerical techniques that can be used to describe strongly correlated two-dimensional systems. These systems are challenging to simulate numerically, as the exponential growth in the size of the Hilbert space with the number of particles means that they can only be solved exactly for very small systems. Recently proposed correlator product states [Phys. Rev. B 80, 245116 (2009)] provide a numerically efficient description which can be used to simulate large two-dimensional systems. In this thesis we apply this method to the two-dimensional quantum Ising model, and the Bose-Hubbard model subject to an artificial magnetic field in the regime where fractional quantum Hall states are predicted to occur.