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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.

In this thesis we aim to study the structural evolution under x-ray illumination in a selection of oxide glass formers as a function of the radiation dose. The irradiated specimens are investigated by means of XPCS experiments and also by means of “exsitu” experiments as luminescence, Raman and x-ray diffraction that have been carried out after the irradiation protocol. As far as we know, the “ex-situ” investigations here reported are the first in the field and have allowed us to evaluate the nature of the point defects, the structural modifications and the nature of the vibrational excitations of the samples exposed to the x-ray dose. The work carried out in the thesis has helped us to elucidate the microscopic evolution of the glass structure under irradiation and to verify whether the transformation can be envisioned as an evolution in the energy landscape, either as an “annealing” or as a “rejuvenation” process.

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.

In this thesis I present the construction of a new apparatus aimed at studying two-component Bose-Einstein condensates (BECs) in the presence of a Rabi coupling, where the two components correspond to internal states of sodium atoms. The coherent mixture, in the miscible regime, also exhibits a metastable excitation consisting in a domain wall of relative phase connecting vortices of different components. Due to the peculiar energy dependence of such a configuration, an attractive force, independent of the vortex distance, is expected, making this system a candidate for mimicking features of quark confinement in QCD. The surface tension of the domain wall structure can be experimentally controlled via the strength of the coupling, allowing to study the system dynamics in different regimes. These include a predicted regime in which, for sufficient high coupling strength, the domain wall breaks and new vortex couples nucleate, providing by itself an interesting experimental realization of spin counterflow dynamical instabilities in a superfluid system, as well as a phenomenon analogous to string breaking in QCD. The choice of sodium as atomic species is motivated by its collisional properties that allow to obtain a perfect spatial superposition between the two miscible components |F = ±1⟩ if trapped by a spin-independent potential, avoiding the known phenomenon of â€TMbuoyancyâ€TM. Studying the dynamics of such systems for sufficiently long times, with a mixture subject to Zeeman differential energy shifts, requires a specific effort to remove magnetic field fluctuations: a rough estimate suggests that in order to maintain the system coherence for a sufficiently long time to study its dynamics, magnetic field fluctuations should be reduced by at least three orders of magnitude compared to typical values observed in laboratory environment. Such attenuations can be obtained by means of multiple layers of Î1⁄4-metal, that is incompatible with the use of ordinary magnetic traps, characterized by large magnetic field gradients on the atoms, due to residual magnetization and saturation of the shielding material. To avoid such effects it is required to either evaporatively cool atoms into an optical dipole trap loaded from a molasses stage, or a hybrid approach by means of which atoms are transferred to a low-gradient quadrupole trap superimposed to the optical trap. Producing BECs with such protocols greatly benefits from an efficient optical molasses cooling stage to prepare the sample in the best conditions of temperature and density before loading atoms into the trap. With this regard, the main limitation of ordinary laser cooling techniques is their reliance on absorption and spontaneous emission cycles, which limits the lowest temperature and highest density that can be reached as a consequence of residual heating effects and photon-reabsorption. An important resource to cope with these limits are dark states. In a broader sense a dark state is a state which does not interact with the exciting light field, and an atom in such a state would be neither subject to the beneficial cooling effects nor to the detrimental effects of light scattering. It is possible, however, to exploit the phenomenon of electromagnetically induced transparency (EIT) to induce a velocity-selective cooling mechanism for which slower atoms, that do not need further cooling, are trapped in a dark state corresponding to a coherent superposition of atomic levels whose excitation probabilities interfere destructively, while the cooling mechanism still applies to the fastest atoms. Among these techniques, gray molasses cooling allows to reach temperatures as low as a few recoil temperatures, while retaining atomic densities useful to reach quantum degeneracy in the subsequent stages of the experiment. In order to exploit this technique, an additional laser source had to be implemented during my thesis. To realize a gray molasses on the sample only |F⟩ → |F − 1⟩ or |F⟩ → |F⟩ transitions can be chosen, requiring blue-detuned laser, in contrast to ordinary (sub)Doppler laser cooling techniques. Both these requirements rule out the use of the D2 transition used for ordinary laser cooling techniques, due to its finely-spaced hyperfine structure. On the other hand, the D1 transition is characterized by a broader level spacing in the hyperfine structure and the absence of higher energy states on the blue side of the |F = 2⟩ → |F' = 2⟩ transition. As part of the work for this thesis, I successfully implemented and characterized gray molasses cooling on the D1 optical line of sodium. The buildup of the new apparatus includes the assembly of a new laser source for laser trapping and cooling on the D2 line, the assembly of the optical table devoted to the frequency and amplitude control of all the laser beams involved in the optical laser cooling procedures as well as the electronic control system. Design and assembly of the UHV and baking procedures for the stainless steel vacuum chamber are also described as well as the laser cooling techniques employed to load the atoms in a Dark-Spot MOT. Regarding the production of BEC, various strategies were attempted for different dipole beam configurations. Dipole traps typically suffer from the tradeoff between capture volume and trap depth at a given power, while hybrid traps usually take advantage of a magnetic trap stage that would not be compatible with the Î1⁄4-metal shielding. Preliminary attempts to reach quantum degeneracy after directly loading the dipole trap from molasses were unsuccessful due to spurious effects. An alternative approach based on a magnetic-shield compatible hybrid trap protocol, in the absence of magnetic trap compression, was successfully implemented.

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.