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.

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.

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.

The R&D program reported in this thesis (develop of cryogenic setups, analysis software and characterizations) has delivered the NUV HD Cryo technology of Silicon Photomultipliers (SiPM) developed in FBK to the DS-20k experiment for the research of Dark Matter. NUV HD Cryo technology currently represents the best cryogenic SiPM performance and fully satisfies the experiment requirements. These developments are relevant also to nEXO experiment and have attracted the attention of other large experiments, such as DUNE, which require large active areas of SiPMs operated in cryogenic noble liquids

No description available.

Biological materials such as wood show outstanding properties due to the self assembly of components from molecular to macroscopic size. An emerging nanotechnology-based strategy consists of the isolation of biological components with size in the range from nanometers to micrometers and of the design of human-driven assembly processes to obtain multifunctional materials. The aim of this thesis was to isolate cellulose nanocrystals, with dimensions of around 4-5 nm in width and some hundred nanometers in length, and investigate their assembly processes through weak interactions among them and with small molecules, like water or ions. Knowing their interaction properties and self-assembly is indeed fundamental in order to fully exploit the potential of nanocellulose in its recently emerging applications. In particular, I focused on cellulose nanocrystals supramolecular self-organization both in absence and presence of water, studying cellulose nanocrystals-based films and hydrogels. In dry conditions, the self-assembly of cellulose nanocrystals on a polylactic support was demonstrated to form few micrometers thick films, characterized by a densely packed arrangement of the crystals leaving elongated cavities of about 0.31 nm cross section between them. These cavities provide the pathway for gaseous 2H2 diffusion. Conversely, these films are impermeable barriers for the transport of gaseous molecules such as O2 and CO2. In aqueous solution, instead, cellulose nanocrystals undergo sonication- or cation-assisted entanglement, forming soft hydrogels. Na+, Ca2+ and Al3+ crosslink the nanocrystals and produce stable hydrogels with structurally ordered domains in which water is confined. Since the gelation process is diffusion controlled, small hydrogel objects with different size and shape have been designed by the coordination-driven assembly of supramolecular rod-like cellulose crystallites, using ionotropic gelation as a methodological approach and Ca2+ as a gelling agent. In parallel to material characterization, particular attention was devoted to the possible exploitation of cellulose nanocrystals-based materials in the biomedical field. In this regard, toxicity studies were performed both on the individual nanocrystals and on the films and hydrogels resulting from their assembly. Moreover, a hybrid cellulose-nanocrystals/chitosan material was developed and characterized, which shows some potential to be used as therapeutic delivery system in the gastrointestinal tract. Indeed, though a mould assisted gelation process, composite hydrogels can be produced, which are degraded by human digestive enzymes and release a model protein according to a biphasic kinetic profile.

Negli ultimi decenni si è vista la nascita di un grande interesse verso l'utilizzo dell'idrogeno come vettore energetico. Le ragioni sono da ricercarsi nelle problematiche sorte in tempi recenti in relazione alle emissioni inquinanti ed al rapido esaurimento delle fonti energetiche. Per poter concepire un'economia basata sull'idrogeno è tuttavia necessario risolvere una serie di problematiche connesse alla sua produzione, immagazzinamento e filtraggio. Il presente lavoro di tesi ha riguardato gli ultimi due punti. In relazione allo stoccaggio del gas, uno dei sistemi più promettenti risulta quello dell'utilizzo d'idruri metallici. Tali materiali presentano ancora una serie di problematiche che ne limitano l'utilizzo pratico, sia in ambito stazionario, che per applicazioni al settore della mobilità. Per superare questi ostacoli è necessaria la comprensione dei meccanismi microscopici con cui avviene la formazione e la dissociazione della fase idruro. Il presente lavoro è stato quindi incentrato sull'approfondimento di tale aspetto, concentrandosi in particolare sul ruolo giocato dai difetti di tipo vacanza in sistemi a base magnesio. Per quanto concerne l'aspetto del filtraggio, le tecniche positroniche sono state impiegate, in concomitanza con altre ad esse complementari, per ottenere una caratterizzazione della porosità, in termini di dimensioni, distribuzione ed interconnettività dei pori, in film di silice da utilizzare per la realizzazione di membrane selettive.

Looking at state of the art of optical devices, it is evident that glass-based rare-earth-activated optical structures represent the technological pillar of a huge number of photonic applications covering Health and Biology, Structural Engineering, Environment Monitoring Systems, Lighting, Laser sources and Quantum Technologies. Among different glass-based systems, a strategic place is assigned to transparent glass-ceramics, nanocomposite materials, which offer specific characteristics of capital importance in photonics. Following this strategy, this PhD thesis exploits tin dioxide (SnO2)-based glass-ceramic activated by erbium ions (Er3+) to put the basis for the fabrication of solid state and integrated lasers. The research discussed in my PhD thesis gives a possible solution to two crucial and decisive points in the development of an optically pumped rare-earth-based laser: (i) the low absorption cross section of the rare-earth ions; (ii) the writing of channels and mirrors in the case of waveguide integrated laser, thanks to the demonstration of two innovative and unique characteristics of SnO2-based transparent glass-ceramics, i.e. luminescence sensitizing and photorefractivity. The role of SnO2 nanocrystals as rare-earth ion luminescence sensitizers allows to overcome the low absorption cross section of the Er3+ ion. The photorefractivity in range of 10-3 of SiO2-SnO2:Er3+ glass-ceramics allows applying the robust direct laser photoinscription technique on the systems to fabricate Bragg gratings and channel waveguides for waveguide integrated lasers. Based on an application-oriented approach, a comprehensive study on SiO2-SnO2:Er3+ glass-ceramic planar waveguides and monoliths, has been carried out. The work covers different research stages and aspects from the material preparation to a complete assessment of systems for the applications employing a rich number and variety of experimental techniques. The energy transfer from SnO2 to Er3+ and the efficient pumping scheme exploiting SnO2 as Er3+ luminescence sensitizers were demonstrated. The relaxation dynamic of the electronic states as well as the location of the dopant and density of states are discussed, and a specific modeling has been developed to the proof of concept realization of the considered devices. The obtained photorefractivity in range of 10-3 allowed the inscription of gratings on the fabricated SiO2-SnO2:Er3+ planar waveguides using UV laser direct writing technique. Exploiting the robust femtosecond laser micromachining, the optical waveguides were inscribed in the fabricated SiO2-SnO2:Er3+ monolithic squares. Another important outcome of this research is the design of a solid state laser with lateral pumping scheme and of an integrated waveguide laser in two different distributed feedback structures using all the parameters measured during the experimental activity.

The aim of this thesis was to study the effects of extremely low frequency (ELF) electromagnetic magnetic fields on potassium currents in neural cell lines ( Neuroblastoma SK-N-BE ), using the whole-cell Patch Clamp technique. Such technique is a sophisticated tool capable to investigate the electrophysiological activity at a single cell, and even at single channel level. The total potassium ion currents through the cell membrane was measured while exposing the cells to a combination of static (DC) and alternate (AC) magnetic fields according to the prediction of the so-called ‘ Ion Resonance Hypothesis ’. For this purpose we have designed and fabricated a magnetic field exposure system reaching a good compromise between magnetic field homogeneity and accessibility to the biological sample under the microscope. The magnetic field exposure system consists of three large orthogonal pairs of square coils surrounding the patch clamp set up and connected to the signal generation unit, able to generate different combinations of static and/or alternate magnetic fields. Such system was characterized in term of field distribution and uniformity through computation and direct field measurements. No statistically significant changes in the potassium ion currents through cell membrane were reveled when the cells were exposed to AC/DC magnetic field combination according to the afore mentioned ‘Ion Resonance Hypothesis’.