This thesis describes a series of synchrotron based X-ray experiments on the lattice dynamics or magnetic ordering of several strongly correlated electron systems. Firstly, it will provide an introduction to the strongly correlated electron materials that were studied. After which a description of the experimental techniques used, specifically resonant X-ray scattering (RXS) and X-ray inelastic scattering (IXS), will be given. Finally the results of these experiments will be set out and evaluated. The experiments were as follows: X-ray inelastic scattering measurements on the effects of fluorine doping on the lattice dynamics of the newly discovered iron pnictide superconducting compound, SmFeAsO0.6F0.35 and its antiferromagnetic parent compound, SmFeAsO. The results from these experiments demonstrate the importance of antiferromagnetic fluctuations in understanding the lattice dynamics of this class of crystals. This result has been demonstrated for the ‘122’ class of pnictide crystals, but until now has not been shown for the ‘1111’ class of pnictides. Resonant X-ray scattering in the vicinity of the Mn L2 and L3 resonant enhancements was used to reassess the magnetic structure of multiferroic TbMnO3. The results indicate that the commonly accepted magnetic structure is modified, with additional a and c axis magnetic components. Therefore the ferroelectric polarisation in TbMnO3 arises from a phase transition between two non-collinear magnetic structures. It was previously believed that this phase transition was between a collinear and a non-collinear magnetic structure. Resonant X-ray scattering measurements were also taken on TbMnO3’s sister compound, DyMnO3. Data was recorded at the Mn K and Dy L3 resonant enhancements. Several unidentified incommensurate reflections, independent of this compound’s magnetic phases, were detected with photon energies close to the Mn K edge. What these reflections represent is still a mystery, although they do make a compelling case for further experimental work.

The development of organic electronic and photonic devices increasingly requires the development of micro- and nano-structured morphologies, which in turn require the development of both prototyping and scalable patterning methods. This thesis presents investigations which explore and develop unconventional patterning techniques for a variety of conjugated polymers and organic molecules, using scanning near-field optical lithography (SNOL), scanning thermal lithography (SThL) and molecular self-assembly. Optimised formation of organic nanostructures is demonstrated, at resolutions which equal or better the current state of the art, with patterning resolution for isolated structures below 60nm for SNOL and 30nm for SThL. SThL in particular is demonstrated as a technique which can achieve serial write-speeds of over 100 μm/s, with significant potential for up-scaling. Furthermore, arbitrarily defined two-dimensional large-area nanostructures up to 20 × 20 μm are demonstrated using SNOL while maintaining both high resolution and the integrity of the probe. The nanostructures fabricated in the course of this work, and others, are characterised using both optical and topographic techniques, primarily atomic force microscopy and near-field microscopy. The detailed formation mechanisms for structures fabricated using SNOL via an in-situ conversion route are systematically investigated and contrasted with other formation routes, resulting in a comprehensive account of the factors affecting structure morphology. In addition, the optimised nanostructures achieved in this work are shown, within this context, to be very close to best achievable with an apertured scanning near-field system.

An important unsolved problem in physics is the nature of electroweak symmetry breaking in the Standard Model. The ATLAS experiment aims to gain insight by studying proton-proton collisions at ps = 14 TeV. In order to dierentiate between dierent theoretical models it is important to measure processes where hadrons are produced, such as the hadronic decay of aW, Z or a Higgs boson. However, these decays produce extremely complex signals in the detector which must be analysed carefully. Jet substructure techniques are presented as a novel approach to analysing hadronic signatures relevant to electroweak symmetry breaking. The potential performance of these techniques is evaluated in detail using simulated ATLAS data. Additionally material related to the use of visualisation software to explore ATLAS data is presented.

Electron-electron correlation, excitation and quantum interference are generally important in attosecond physics, especially for imaging of atoms and molecules. These are the main topics addressed in this thesis, in the context of laser-induced nonsequential double ionization (NSDI). Excitation is the most extensive topic of this work and is addressed within a rigorous, semi-analytic study of the recollision-excitation with subsequent tunneling ionization (RESI) mechanism in laser-induced nonsequential double ionization (NSDI). This is the most comprehensive study of this mechanism performed in the context of the strong-field approximation to the preset date. Subsequently, we investigate potential imaging applications, by computing electron momentum distributions of atoms and molecules. For atoms, we show that the RESI electron momentum distributions depends very critically on the bound state wave function. For molecules, we address the influence of the molecular orbital geometry and of the molecular alignment with respect to the laser-field polarization, by computing the electron momentum distributions of N2 and Li2. We show that the electron-momentum distributions exhibit interference maxima and minima, either due to the electron emission at spatially separated centers, or to the orbital geometry, such as nodes of the atomic wavefunction. In this latter case, we do not restrict ourself only to RESI, and we also compute the electron momentum distributions of N2 for electron-impact ionization, in which we also observe two-center interference patterns when the molecule is aligned along the laserfield polarization direction. The above-mentioned momentum constraints, together with the strong dependence of the distributions on the bound states involved, the molecular orbital geometry and the molecular alignment angle may be important for singling out the RESI mechanism in actual physical situations and using NSDI in ultra-fast imaging. In the final chapter, we present the first step taken by us in order to address the above-stated issues using an approach beyond the strong field approximation.

This thesis reports on the development of a laser system for the manipulation of molecules using the optical dipole force. The centre-of-mass motion of molecules within the deep optical lattices created by the laser system, was probed using coherent Rayleigh scattering (CRS) and compared with simulations of these processes. The laser system was constructed to produce two, temporally coincident, pulsed beams with durations of hundreds of nanoseconds. The frequency difference between the two beams was controlled to be on the order of 1 GHz. This frequency control was produced by the construction of a low power ( 20 mW) Nd:YVO4 microchiptype laser which was frequency chirped by rapidly changing cavity length via an intra-cavity electro-optic crystal. The deleterious effects of intensity modulation induced by this process, were overcome by the design of an injection locking system with a free running semiconductor diode laser. This master slave laser system was pulse amplified to the required intensity in a fibre amplifier and a Nd:YAG flashlamp pumped amplifier system with a total gain of 109 maintaining the frequency characteristics of the low power laser system. The motion of molecules trapped in the optical lattice produced by the laser system was probed using CRS. Long pulse CRS was performed on xenon and octane gases utilising 100-200 ns pulses with a flat-top profile.

This thesis discusses various schemes and protocols for quantum information processing in mesoscopic systems with particular focus on using the spin of a particle as the bearer of information. The first chapter introduce various aspects of the field of quantum information used in this thesis such as qubits, entanglement, its quantification, quantum logic gates and entanglement swapping. In this chapter concepts such as AKLT states, decoherence and adiabatic elimination are introduced as they will be relevant in the thesis. In chapter 2 we introduce the Quantum Dots as the solid state system that will primarily be used as the hardware for the development of Quantum Information Processing (QIP). The different properties of quantum dots depending on their size are discussed. The exchange interaction between tunnel coupled quantum dots and the background of quantum computation in quantum dots is described. The principal sources of decoherence and the measurement techniques for spin qubits are presented. In chapter 3, carbon nanowires filled with N@C60 dimers are studied to analyse the entanglement between nuclear spins. The dimer is modelled as a two coupled nuclear spin- electron spin pair with a Heisenberg interaction. The entanglement have been studied depending on the temperature and the intensity of an external magnetic field. Witnessing the entanglement, and particularly bound entanglement are discussed. In chapter 4, the way to extract a singlet from a quantum dot is explored. The system that we model will be consisting of a triple dot and analyse the best way to get the singlet out, with each electron in a separate dot. The chief motivation is to create a singlet between separate dots in a time-scale much faster than that given by spinspin exchange interactions. In chapter 5, quantum logic gates in a triple dot system has been studied. Such gates have been widely studied in double and single quantum dots. Motivated by the advent of experimental set ups of triple dots, we have studied the natural quantum gates that came out of a triple dot system. There are still two spin quantum bits in the three dots and there is an empty intervening dot, which imparts the scheme some advantages, as well as a substantial difference from the class of schemes studied so far. In chapter 6, we model a large square dot. As we describe in chapter 2, the properties of the large dots make them behave with some interesting properties such as hosting Wigner molecules of electrons inside. We explore the application of these structures for quantum information processing. We show here how to get singlet/triplet measurement, entanglement swapping, and how to prepare a 1D AKLT state, using the square dot as a construction block of the system. Finally in chapter 7 conclusions and further work. Here we indicate the further work that could be done with the knowledge present in this thesis and motivated by future advances in the technology.

Quantum Molecular dynamics (MD) simulations have been widely used to examine the dynamics of interactions between electrons and ions. The most commonly used MD method is the Born-Oppenheimer (BO) approximation, which assumes that the electronic states always stay on the ground-state energy surface of any given ionic configuration during the course of the simulation. The BO approximation, however, is not appropriate for studies of systems that are out of equilibrium, such as electron transport processes. One way of allowing an MD simulation to explore the non-equilibrium and excited states is to use the Ehrenfest approximation, which gives a full time-dependent quantum mechanical treatment of electrons, while regarding the ions as classical particles. This thesis gives a careful derivation of the equations of motion (EoM) in Ehrenfest dynamics, in the context of the Time-Dependent Density Functional Theory represented in a non- orthogonal and incomplete basis centered on the moving ions. The EoM were implemented in an existing ab initio electronic structure code Plato. Various propagators for solving the electronic EoM were studied and compared. A micro- canonical model based on the Ehrenfest MD for simulating electron transport processes has been developed. Extensive real-time transport studies were performed on aromatic hydrocarbon compounds attached to graphene nanoribbon leads. A self-consistent non-orthogonal tight-binding model was used to enable large-scale simulations with reasonable computational cost. The quasi-steady-state currents together with the current induced dynamical effects were measured from the simulations and analysed. The quasi-steady-state currents were compared with the steady-state solutions obtained from a time-independent non-equilibrium Green functions method commonly used by the electron transport community.

This thesis discusses the measurement of the inclusive b-jet cross-section using the 2010 ATLAS dataset and the measurement of di-b-jet cross-sections using the 2011 dataset. The inclusive b-jet analysis measured the pT spectrum of b-jets in the range 20<pT<400 GeV in four rapidity ranges, |y|<0.3, 0.3 < |y| < 0.8, 0.8 < |y| < 1.2 and 1.2 < |y| < 2.1. Good agreement was observed between data and the NLO theory predictions generated by the POWHEG and MC@NLO Monte Carlo generators. However, when the cross-section measurement was split into the |y| regions, MC@NLO showed some shape differences with respect to data. The di-b-jet analysis using the 2011 ATLAS dataset measured the di-b-jet cross-section with respect to six different variables. This analysis investigates regions of phase space that are sensitive to different bb production mechanisms. It was found that Monte Carlo simulation predicts back- to-back b-jet topologies well. Situations where the b-jets are closer together are more challenging to model and both MC@NLO and POWHEG overpredict the rate of such events.

Nuclear motion resonant states of triatomic molecules are calculated using an L2 method known as Complex Absorbing Potential (CAP). This method is implemented in a new program named RES3D which includes a new automatic procedure to obtain the resonant states’ energies and lifetimes, allowing for the first time the quantification of the results’ accuracy through a consistency test across different CAP functional forms. Its implementation is described in detail. Validation tests consisting of a comparison of HOCl resonances calculated with RES3D with those available in the literature, are presented. The largest calculations to date of the vibrational states of H+3 and D2H+ of all bound state eigenvectors and up to about 2000 cm−1 above dissociation are also presented. The results of these calculations are analysed through studies of the convergence of bound states, the calculation of relevant observables, and the visual analysis of wavefunctions. Based on eigenvectors obtained from these calculations, vibrational resonances for H+3 and D2H+, as well as H+3 at J = 3 are calculated with RES3D. D2H+ is used to study the resonances in multi-channel systems by investigating two energy regions: the one where D2 + H+ is the only dissociation product and the one where HD + D+ can also be formed. Branching ratios are obtained in the latter case by using different CAPs. It is shown that H+3 and D2H+ support narrow Feshbach-type resonances. The findings from the study of resonant states made using RES3D and possible technical improvements to the program are discussed. A brief description of the work currently being done to use RES3D in an attempt to fully characterise the spectrum of H2O is also presented.

Updates to the ATLAS fast simulation software are presented which improve the flexibility of its calorimeter and reconstructor objects allowing the easy implementation of new and unforeseen detector effects. Both hot and dead cell types are studied as initial examples and can be seen to be working as expected. A suite of jet finding algorithms known as ‘FastJet’ is introduced and linked into the ATLAS code framework to help unify the description of jets between fast and full simulations as well as in the reconstruction of data. Preparations for an early-data supersymmetry search in the 0-lepton, jets and ETmiss T channel are presented which, in the absence of a study of the background systematics, show the validity of the channel in detecting the ‘SU3’ mSUGRA benchmark point above the combined standard model background. The most up-to-date publication observes good agreement between the simulated SM background and data up to values of ETmiss ~100 GeV and Meff ~1500 GeV showing a good understanding of both detector and physics simulation and that the real ATLAS detector is performing as expected. The first ATLAS inclusive measurement of charged particle multiplicities in events with nch ≥ 1 within the kinematic range pT > 500 GeV and |η| < 2.5 is discussed. With a measured charged particle multiplicity per event and per unit of pseudorapidity at η = 0 of 1.333 ± 0.003(stat.) ±0.040(syst.) being some 5-15% higher than predicted, clear differences are evident between the Monte Carlo predictions and what is observed in the data. Contributions from the author including trigger efficiency studies, a ‘Rivet’ analysis routine, a simple simulation of the MBTS as well as the creation of a fast trigger simulation of the MBTS triggers L1_MBTS_1, L1_MBTS_2 and L1_MBTS_1_1 are detailed.