This thesis describes the development of an experiment to study coherent population transfer between ground states, and between ground and Rydberg states, in ultracold atoms. In order to study coherent transfer between hyperfine ground states a pair of phase stable Raman beams is required. Both beams are derived from a single master laser before being spatially separated into individual components using a novel Faraday filtering technique. The frequency dependent Faraday effect in an isotopically pure thermal vapour is exploited to rotate the plane of polarisation of each Raman component such that they may be separated using a polarising beam splitter. The Raman beams are applied to a sample of ultracold atoms and evidence of coherent population transfer is observed. Rydberg states offer an ideal tool for electrometry; the electric field induced Rydberg energy level shift scales with the seventh power of the principle quantum number. Electromagnetically induced transparency (EIT) is used to map Rydberg energy level shifts onto a ground state transition. EIT in a thermal vapour cell also provides a novel method of stabilising the Rydberg coupling laser. The Rydberg energy level shift is highly sensitive to the electric field produced by adsorbates bonded to a nearby dielectric surface. These effects are found to be time dependent and can be eliminated if the electric field is applied transiently. The measured electric field is compared to that calculated by numerical solution of Laplace's equation; the bulk dielectric is found to have a strong effect on the local electric field experienced by the atoms. The exaggerated properties of Rydberg states make these systems ideal for quantum information processing and precision electrometry.

In this work we investigate the potential of controlling cold (O(K)−mK) and ultracold (mK-μK) atom-molecule collisions by tuning scattering states across Feshbach resonances using magnetic fields. We are interested in particular in the prospect of suppressing the often undesirable inelastic collisions. The He-O_2 system provides the vehicle for our study. We calculate bound and quasi-bound states of several isotopic combinations, including their Zeeman structure, to reveal the underlaying pattern for easier characterization of quasi-bound states in terms of rigorous and approximately good quantum numbers. These calculations also help us locate the fields at which zero-energy resonances will occur. Scattering calculations are then performed for collisions of 3^He and 4^He with {16}^O_2 at fixed (1 μK) energy but varying magnetic field. The field is varied to sweep the scattering state across resonance. At low and ultralow energies we enter the Wigner threshold regime where the S-partial wave dominates the wavefunction. The cross sections, and the real and imaginary parts of the scattering length, vary dramatically across resonance. Their profiles are used to analyze the resonances. In a highlight of our results we show that dramatic suppression of inelastic cross sections occur for 4^He-{16}^O_2 . The resonances are relatively wide (of order 100 Gauss), with suppression of inelastic scattering over a similarly wide range of fields and for temperatures ranging from 10 mK down to 1 μK. We conclude that under certain conditions it is possible to almost completely eliminate inelastic collisions. This is potentially very important for cooling techniques, such as evaporative and sympathetic cooling, that require efficient elastic cross sections. Suppression of inelastic collisions can not only increase thermalization efficiency but it can also result in longer trap-lifetimes by reducing transitions to untrapable states.

This thesis presents the first realisation of a new type of hybrid quantum device based on spintronic technology. We demonstrate an interaction between the magnetic fringing fields produced by domain walls within planar permalloy nanowires and a cloud of ultracold Rubidium 87 atoms. This interaction is manifested through the realisation of a magnetic atom mirror produced by a two-dimensional domain wall array. The interaction is tuned through the reconfiguration of the micromagnetic structure. Analytic modelling of the fringing fields is developed and shows good agreement with calculations based on micromagnetically simulated structures. The accurate and rapid calculation of the fringing fields permits simulation of the resulting atom dynamics, which agrees well with data. In turn, we use the atom dynamics as a probe of the micromagnetic reconfiguration processes that take place and observe a collective behaviour which is both reliably reproducible and in agreement with alternative, conventional magnetometry. We also observe evidence of stochastic behaviour, characteristic of superparamagnetic systems. We consider the development of a more advanced spintronics-based atom chip which will allow for the creation of extremely tight mobile atom traps. We consider the problems associated with ensuring that the trapping potential is adiabatic, sufficiently deep, and technically feasible. In particular we examine techniques to circumvent losses due to Majorana spin-flip transitions. As a result of this study we propose a novel scheme for creating time-averaged potentials via the piezoelectric actuation of magnetic field sources. We show that this technique presents significant fundamental and technical advantages over conventional time-averaging schemes.

Naturally occurring grain boundary interfaces greatly influence important characteristics of many materials including their mechanical, electrical and magnetic properties. The atomic structure of such grain boundaries, while crucial to their behaviour, are inaccessible to most experimental techniques as they are internal to the material. Theoretical studies are complicated by the existence of multiple structures for a given grain boundary. Data from an X-ray diffraction experiment is presented, along with the model used for simulated scattering from Keating energy minimised grain boundary structures. The X-ray diffraction data was measured using a (2+3)-type diffractometer on beamline I07 of the Diamond Light Source. The traditional way to measure the integrated intensity from an X-ray diffraction experiment is to perform a rocking scan. By use of a large 2D area PILATUS detector, an alternative method of measuring diffraction data, where the sample remains fixed, can be implemented. A comparison of the different techniques shows that the stationary scan improves the reliability and shortens the measuring time by almost an order of magnitude. The theory of crystal truncation rod scattering is extended to account for the bicrystallography of the sample, which gives rise to two overlapping rods; one from each crystal. Simulated X-ray scattering from Keating energy minimised grain boundaries is compared with experimental data. The simulated scattering, which has atomic sensitivity, is used to discriminate between potential structures based on the statistical goodness of fit with the data. Finally, a custom designed diffraction chamber was built allowing users to perform lensless Fourier transform holography experiments on the branchline of I06 at the Diamond Light Source. Preliminary data is presented and data analysis techniques discussed. Phase retrieval algorithms do not yield any further high resolution reconstructions due to the noise levels of the hologram.

The breaking of the N=20 shell gap in neutron-rich nuclei is investigated by studying the single-particle structure of 27Ne via neutron transfer onto a 26Ne beam. The observation of low-lying negative parity states in 27Ne above the 3/2+ ground state is further evidence of the raising of the νd3/2 orbital that is seen in other neutron-rich nuclei in the N=20 region. The previously unseen 7/2− state has been identified as unbound by 331 keV and lies above the already known 3/2− level. The measurements of the present work contradict SDPF-M Monte-Carlo Shell Model predictions, but are in good agreement with WBP shell model calculations in which the single-particle energies of the pf shell are artificially lowered by 1 MeV. This modification was made to mimic the closing of the N = 20 shell gap in neutron-rich nuclei. The predictions of the modifiedWBP calculations are also in agreement with experimental measurements in the adjacent nuclei of 25Ne and 29Mg. The calculations show that core-excited configurations play a significant role in both the 3/2+ ground state and the 7/2− intruder state in 27Ne.

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