The AEgIS experiment pursues the ambitious goal of measuring for the first time the gravitational pull on neutral antimatter. The envisioned method consists in producing a beam of cold anti-hydrogen and measuring the deflection of its free fall by means of a Moiré deflectometer. To do so the pulsed production of abundant cold anti-hydrogen is paramount, therefore the charge exchange production mechanism has been elected as the most promising candidate production method. Performing the charge exchange anti-hydrogen production requires access to an abundant source of cold positronium which can be achieved by the employment of oxide-coated nanochanneled silica plates (NCPs). We spend chapter 1 formulating a classical model of positronium production and thermalisation in NCPs and validating it by testing it against the available experimental data. In chapter 2 we describe the measurement of the energy spectrum of positronium produced by nanochanneled plates using the beam produced by the SURF machine. We then compare the measured energy spectra with the model proposed in chapter 1 showing, in the comparison, the indication of a transition during thermalisation process to a regime where quantum phenomena become significant. We describe in detail in chapter 3 several positronium spectroscopy measurements that we performed during the course of the last three years by employing the positron beam line of the experiment AEgIS. We will the proceed to illustrate an improved version of the detrending technique commonly employed in signal analysis which, applied to the analysis of SSPALS spectra, improves the achievable precision on the experimental results. In chapter 4 we describe an innovative approach that we are currently pursuing to employ the detector FACT, part of the AEgIS apparatus, to confirm the successful production of anti-hydrogen.

Disorder is an inherent component of real materials, with significant implications for their application in functional devices. Despite this, the theoretical modelling of disorder remains restricted, primarily due to the large simulation cells required to adequately represent disordered systems, and the associated computational costs. This has been remedied in part by the increased availability of resources for high performance computing. In this thesis, using a combination of computational techniques, primarily density functional theory and ab initio as well as classical molecular dynamics, we investigate disorder in two broad categories – physical and chemical disorder, in three distinct classes of materials: palladium nanoparticles, the negative thermal expansion cuprite Ag2O and the complex quaternary chalcogenide Cu2ZnSnS4, known commonly as kesterite. The ‘physical’ disorder discussed in the thesis constitutes shape- and adsorption-induced mechanical softening on the surface of Palladium nanocrystals used for nanocatalysis. This includes one study on the the adsorption of organic capping agents, and another on the adsorption of oxygen molecules and the subsequent oxidation of Pd. In the former, it was observed that the strain effect due to adsorption-induced surface disorder is significantly greater than that due to variations in surface termination, i.e. nanoparticle shape. Moreover in the latter case, different crystallographic facets with different degrees of disorder were found to affect the spin-flip induced activation of oxygen atoms, relevant to the catalytic oxygen reduction reaction in hydrogen fuel cells. In each case, the computational results were combined with a sophisticated, phenomenological whole powder pattern modeling of X-ray diffraction data primarily from synchrotron radiation, leading to an accurate characterization of the Debye-Waller coefficient, which was established as a reliable metric for disorder in crystalline systems. In the case of Ag2O instead, we demonstrated that the large experimental Debye-Waller coefficient was due to thermal diffuse scattering arising from the strong distortion of the Ag4O coordination tetrahedra. The second form of disorder which was investigated is ‘chemical’ disorder, which refers to cation disorder in the quaternary chalcogenide Cu2ZnSnS4 studied for its performance as a thermoelectric material. Similar to the studies on palladium, the disorder was quantified through the Debye-Waller coefficient using molecular dynamics simulations, this time from ab initio methods, and compared with X-ray diffraction data from a synchrotron source. The ordered phase of CZTS is known to crystallize in a tetragonal phase, with alternating Cu-Zn and Cu-Sn cation layers sandwiched between sulfur layers. Two forms of cation disorder were studied: disorder only in the Cu-Zn layer, leading to a disordered tetragonal phase, and full cation site randomization, leading to a disordered cubic polymorph. In the former case, it was found that the higher symmetry of the disordered tetragonal structure led to an average symmetrization of the nearest neighborhood of each individual cation, as a result of which there was a convergence of bands at the valence band maximum, leading to an experimentally observed increase in p-type carrier concentration. In the case of CZTS with full cation disorder, inhomogenous bond led to favorable modifications of the electronic and phonon properties, allowing for a simultaneous improvement of the experimentally measured electrical and thermal conductivities as well as the Seebeck coefficients. Finally, by studying the atypical electronic band structure of this cubic polymorph, we were able to identify topologically non-trivial behavior evidence of bulk band inversion, robust surface states, and an adiabatically continuous connection to a known TI phase. As such, we were able predict disordered cubic CZTS to be the first disorder-induced topological Anderson insulator in a real material system.

This thesis work covers scientific and technological advancements in integrated silicon photonics circuits aimed at developing an All-On-Chip device for quantum photonics experiments. The work has been carried out within the framework of project SiQuro, where the Silicon-On-Insulator platform is chosen to integrate all the components of an optical bench necessary for a quantum experiment into a single chip. The problem of generating photon pairs have been addressed by studying second order polarisation effects in strained silicon with the aim to realize a bright photon pairs source based on Spontaneous Down Conversion. The study revealed that processes other than the Pockels effect are responsible for the non-linearity coefficients previously measured, suggesting to look for other candidate processes for the generation of photon pairs, as third order non-linear processes. To provide with the bright coherent source necessary to enable non-linear processes the integration of a hybrid III-V-silicon mode-locked laser has also been studied. During this study, technological novelties have also been developed by modelling the wedge profile obtained during the wet etching of silicon glass materials to engineer 3D structures. In parallel, the physics of whispering gallery mode resonators, both in silicon and in silicon glass materials, have been addressed. Silicon nitride Ultra High-Quality resonators have been demonstrated by using a strip-loaded configuration, while relative tuning of resonant modes has been demonstrated in an all-optical experiment exploiting the thermo-optic effect. This work represents a step forward in the study of the physics and applications of silicon-based lightwave circuits for integrated photonics.

Simulating rare structural rearrangements of macromolecules with classical computational methods, such as Molecular Dynamics (MD), is an outstanding challenge. A multitude of technological advancements, from development of petaFLOPS supercomputers to advent of various enhance sampling methods, has granted access to time intervals of microseconds and even milliseconds in recent years. Yet, many key events occur on exponentially longer timescales. Here, path sampling techniques have the advantage of focusing the computational power on barrier-crossing trajectories, but generating uncorrelated transition paths that explore significantly different conformational regions remains a problem. To address this issue, we devised a hybrid path-sampling scheme, graph-Transition Path Sampling (gTPS), that generates the trial transition pathways using a quantum annealer. We first employ a classical computer to perform an uncharted exploration of the conformational space using a data-driven MD method. The dataset is then post-processed using a path-integral-based method to obtain a coarse-grained network representation of reactive pathways. By resorting to quantum annealing, the entire ensemble of these pathways can be encoded into a superposition in the initial quantum state of the annealer. Finally, by performing the quantum adiabatic transition on the state of the annealer, one can potentially generate/sample uncorrelated paths while they retain a high statistical probability (follow low free energy regions). We have first validated this scheme on a prototypically simple transition (α_R↔C_5 of alanine dipeptide) which could be extensively characterized on a desktop computer. Subsequently, we scaled up in complexity by generating a protein conformational transition (Bovine Pancreatic Trypsin Inhibitor - BPTI) that occurs on the millisecond timescale, obtaining results that match those of the Anton special-purpose supercomputer. Finally, we dicuss our current investigations on the application of gTPS to the unfolding process of headpiece subdomain of Villin and BPTI. Despite limitations due to the available quantum hardware, our study highlights how realistic biomolecular simulations provide a potentially impactful new ground for applying, testing, and advancing quantum technologies.

One of the main reasons which makes Bose-Einstein condensates a successful topic of research is their flexibility for creating systems whose Hamiltonian can be engineered almost at will. A particularly relevant research topic in the field of Bose–Einstein condensation concerns the realization of binary mixtures in the presence of coherent coupling Ω. These systems show properties having analogies with the formation of stripe phases, which are related to supersolidity, or with the formation of domain walls, which are related to quark confinement in quantum chromodynamics. Technically, the realization of coherently coupled binary mixtures requires a deep knowledge of the system properties, even in absence of coherent coupling between the two states, and a highly precise control of the magnetic field. Both these topics are treated in this research work, which aims to lay the foundation for experimental studies in resonantly-coupled spinor BECs. More in detail, the simplest collective oscillation, i.e., the spin-dipole (SD) oscillation and the static SD polarizability are studied to test the miscibility properties of the system and its response to external perturbation of the trapping potentials, both at zero and at finite temperature in order to characterize the behaviour of the system at Ω = 0. This work also reports the theoretical study done to design a magnetic shield able to guarantee a precise control of the environmental magnetic field and suitable to be used to study the binary mixture in the presence of coherent coupling.

The PhD thesis work here presented was carried out within the SiQuro project at the Nanoscience laboratory of the University of Trento. The project started in September 2013 and lasted four years. It was funded by the Provincia Autonoma di Trento (PAT). SiQuro’s goal was to bring the quantum world into integrated photonics by using the silicon platform and, therefore, permitting the integration of quantum photonics with electronics. The vision was to have low cost and mass manufacturable integrated quantum photonic circuits for a variety of different applications in quantum computing and secure communications. It must be said that SiQuro was a challenging and ambitious project, nevertheless important achievements in the quantum photonics arena were reached. My thesis is concentrated on the generation, manipulation and detection of quantum states of light. On one side, this was carried on in strained silicon waveguides, with the final goal to generate MIR entangled photon pairs via SPDC. Alongside, the generation and manipulation of correlated photon pair sources by means of spontaneous FWM in traditional silicon waveguides and microring resonators at telecom wavelength was also investigated. For the detection of MIR photon pairs, a suitable detection unit was developed as well. Moreover, even though the long-term goal of the project was the realization of a silicon quantum photonic circuit, I also implemented free-space quantum optical experiments. For this, I exploited a bulk nonlinear crystal, namely lithium niobate (LiNbO3), which has a well-known sizeable χ(2) nonlinearity.

Microscopically disordered materials are at the core of an increasing number of new material technologies, but crucial limitations in their applications come from the physical aging of their properties and the extreme sensitivity on the system's history, which stem from the their intrinsically out of equilibrium nature. A clear understanding of the aging phenomenon, as well as the effects of the release of internal stresses acting at different length-scales, are still lacking. In this Thesis the slow dynamics of disordered systems is investigated at different length-scales ranging from the micrometre length-scale probed in optical experiments to length-scales of few angstroms probed in wide angle X-ray experiments. The time evolution of the probed out of equilibrium dynamics is thoroughly studied in different glasses exploiting the multi speckle photon correlation technique with different sources. The investigated materials are a set of strong glass-formers (materials that can be found in a wide variety of common glassware) and colloidal suspensions at high volume fractions in an arrested state. The latter class of materials are known as soft glasses and in recent years they are earning great interest and can be found in a lot of industrial products (e.g. wall paint, ink, chocolate) or in production processes (e.g. ceramics). Despite the differences between the probed systems and their production protocols, it is here shown that in all the studied materials the microscopic dynamics displays common trends and that it is strongly connected to the relaxation of the stresses that have remained trapped in these systems after their production.

The dynamics of systems out of equilibrium, such as the phase transition process, are very rich, and related to largely scalable problems, from very small ultracold gases to large expanding galaxies. Quantum low-dimensional systems show interesting features, notably different from the canonical three-dimensional case. Bose-Einstein condensates are very good platforms to study macroscopic quantum phenomena. These three points describe well the motivation behind the study presented in this work. In this thesis, some dynamical problems of trapped and uniform condensates are studied, both at zero and finite temperature. In particular, we focus on the analysis of the propagation of linear and nonlinear excitations in a quasi-1D and in quasi-2D systems. In the first case, we are able to correctly describe the dynamics of a solitonic vortex in an elongated condensate, as measured by Serafini et al. [Phys. Rev. Lett. 115, 170402 (2015)]. In the second case, we reproduce the decay rate of a phase-imprinted soliton (collaboration with Birmingham), and assess its dependence on the temperature. We also replicate the propagation speed of sound waves over a wide range of temperatures as in Ville et al. [arXiv:1804.04037] (collaboration with Collà ̈ge de France). The result of this analysis is included in Ota et al. [arXiv:1804.04032], which is currently under revision. In uniform low-dimensional systems Bose-Einstein condensation is technically not possible, and in two dimensions it is replaced by the Berezinskii-Kosterlitz-Thouless superfluid phase transition. We study its critical properties by analysing the spontaneous generation of vortices during a quench, produced via the Kibble-Zurek mechanism. This procedure predicts, for any dimension, the scaling for the density of defects formed during a fast transition, when the system is not adiabatically following the control parameter, and regions of phase inhomogeneity are formed. We address the role of reduced dimensionality on this process. All finite temperature simulations are performed by means of the stochastic (projected) Gross-Pitaevskii equation, a model fully incorporating density and phase fluctuations for weakly interacting Bose gases.

The atomic mean square displacement (MSD,  ̄(σ_i^2 ) ) is often used in computational materials science studies to calculate measurable properties from the atomic trajectories of simulations; for example, the diffusion coefficient, which according to Einstein relations (Einstein 1905) on the random walk is 1/6 of the slope of the trend of  ̄(σ_i^2 ) vs. time (Chandler 1987). Equally relevant is the mean square relative displacement (MSRD,  ̄(σ_ij^2 )), used in X-ray Spectroscopies, mainly EXAFS, to describe the atomic disorder in solids (Calvin 2013) (Fornasini 2014). Less known is the relevance of the MSRD in X-ray scattering from nanoparticles. In particular, in Total Scattering methods (Pair Distribution Function and Debye Scattering Equation), which rely on an atomistic description of the nanoparticles, the MSRD is the key to distinguish dynamic (thermal) and static disorder (Krivoglaz 1969) (Kuhs 2006). Interestingly, the trend of the MRSD with the distance is characteristic of the nanoparticle shape, an aspect investigated in some detail in this Thesis work. More generally it can be shown that beyond the expected effect of nanocrystal size, the shape alters the contribution of the surface, which is quite relevant for the MSRD. The importance of the shape and of the surface region holds also in case of clusters of nanoparticles, not only in isolated particles. Besides the MSRD, the atomic configurations simulated by molecular dynamics (MD) can also be used to calculate the so-called Warren plot (or diagram), originally introduced in the seminal work of Warren & Averbach of the †̃50s to describe the effects of plastic deformation in metals (Warren B.E. 1950). Recent work has shown how to obtain Warren plots from the analysis of the diffraction line profiles according to the Whole Powder Pattern Modelling (WPPM) (L. M. Scardi P. 2002) (Scardi P 2017) (P. E.-W. Scardi 2018), in particular from the analysis of the strain component of the diffraction peak profile broadening. As proposed in this work, If the Warren plot can be calculated directly from MD simulations, then it is possible to proceed backwards, and construct more reliable strain functions from an atomistic knowledge of the local atomic displacement caused by static and dynamic disorder components. This thesis is divided in two main parts, discussing two different but complementary topics: atomistic modelling and calculations of displacement quantities, application of the above results to experimental case studies, based on the modelling of diffraction data from nanocrystalline systems. We start by describing the atomistic simulations and vibrational properties calculated for several atomic configurations. The main case study concerns Palladium nanoparticles of different sizes and shapes, for which we show that vibrational properties and correlation properties between atoms pairs are greatly influenced by the geometric shape of the nanoparticle and to a lesser extent by their size. The interest is on truncated cubes, i.e. cubes whose edges and corners are progressively removed, as in the series of so-called Wulff solids, ranging from the cubic to the octahedral shape (Wulff G. 1901). As shown in (ii), these are the object of several experimental studies. The developed methodologies are nevertheless applicable to other cases, like the clusters of nanocrystals observed in powders produced by high-energy ball milling, which is also a topic discussed in (ii). The work aims to show a general approach to atomistic modelling, both for isolated nanoparticles with definite shapes, and grains of unspecified shape in plastically deformed polycrystalline materials. We then use the values for displacement quantities (e.g., MSD, MSRD) calculated for the simulated systems to compare them to the experimental results. An underlying fact that seems to hold in all the different cases is that the surface behaviour of nanomaterials has the largest influence on the displacement quantities. For isolated particles we observe strong correlation between displacement quantities and the shape; whereas in the case of a nanocrystalline grain clusters (Figure 1 1) we see that no matter the defects inside the grain, the main contribution to MSRD is given by the grain boundary.

In the context of the electrification of the chemical industry, this thesis sets itself the goal of studying two promising plasma reactors: a nanosecond repetitively pulsed (NRP) discharge and a microwave discharge. The NRP reactor has been investigated for the dissociation of CO2. The microwave discharge has been used for studies of vibrational energy loading into N2 , as a first step towards the non-thermal synthesis of NO for fertilizer production. The complicated system that a non-equilibrium plasma represents requires sophisticated diagnostics. Such diagnostics have to be species specific and provide spatial and time resolved information about the quantities of interest, such as temperature (vibrational and rotational), product concentration and energy deposition. Given these require ments, diagnostics based upon the use of pulsed lasers are usually employed to study systems where fast kinetics are at play. The diagnostics of choice are Laser Induced Fluorescence (LIF) and vibrational Raman scattering.