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Public display of deposited theses

Presentació d'al·legacions a una tesi doctoral en el termini d'exposició pública

In accordance with the Academic Regulations for Doctoral Studies, doctors may request access to a doctoral thesis in deposit for consultation and, if there are, to send to the Permanent Commission of the Doctoral School the observations and allegations that they consider opportune on the content.

 

DOCTORAL DEGREE IN APPLIED MATHEMATICS

  • PORRO MARTORELL, OLGA: A Hesitant Fuzzy Perceptual-Based Approach to Model Linguistic Assessments
    Author: PORRO MARTORELL, OLGA
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN APPLIED MATHEMATICS
    Department: Department of Mathematics (MAT)
    Mode: Normal
    Deposit date: 04/03/2021
    Deposit END date: 18/03/2021
    Thesis director: SANCHEZ SOLER, MONICA | AGELL JANÉ, NÚRIA
    Committee:
         PRESIDENT: TRAVÉ-MASSUYÈS, LOUISE
         SECRETARI: GIBERT OLIVERAS, CARINA
         VOCAL: VALLS MATEU, AÏDA
    Thesis abstract: Multiple-criteria or multiple-attribute group decision-making is a sub-field of operations research that seek to find a common and representative solution given the preferences elicited by a pre-defined group, over a set of alternatives and with respect to a set of coherent criteria (or attributes). Recently, the modelling of natural language in these processes has captured the attention of many researchers. Most of the evaluations in a group-decision making context are inherently imprecise, incomplete or vague, and therefore, experts feel more comfortable using their language rather than numerical values. The use of hesitant fuzzy linguistic term sets is one of the recent tools that enables the modelling of linguistic assessments in multiple-criteria decision-making. Nonetheless, advances in hesitant linguistic multi-attribute group decision making require the development of structures flexible enough to deal with unbalanced and multi-granular linguistic information. More tools are needed in order to really grasp the differences in the qualitative reasoning processes of each individual. This thesis, firstly, introduces a perceptual-based distance able to capture differences between unbalanced linguistic assessments, which is based on a lattice structure of hesitant fuzzy linguistic terms. Secondly, this distance is used to define a perceptual-based centroid or central opinion which, in turn, is used to define a consensus measure or degree of agreement within the group. Thirdly, with the aim to deal with multi-perceptual group decision-making contexts, where each decision maker has its own qualitative reasoning approach, a perceptual-based transformation function and a projected algebraic structure are defined. The developed tools can deal with different multi-granularity linguistic environments. Two applications are presented to demonstrate the utility, relevancy and feasibility of the methods. On the one hand, a specific perceptual-based classification and ranking method is introduced and applied to a real group decision making problem in an educational setting. This framework is used to classify and rank a set of secondary students according to their degree of entrepreneurial competency, which is based on real data provided by the Andorra Government. On the other hand, an extended fuzzy multi-perceptual linguistic TOPSIS is designed and applied to a real group decision making problem in the context of smart city governance. This perceptual extension is used to assess the criteria governing the strategic decision making process of energy multinational companies when deciding where to expand its sustainable services and products.

DOCTORAL DEGREE IN COMPUTATIONAL AND APPLIED PHYSICS

  • AZNAR LUQUE, ARACELI: Barocaloric effects at first-order phase transitions
    Author: AZNAR LUQUE, ARACELI
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN COMPUTATIONAL AND APPLIED PHYSICS
    Department: Department of Applied Physics (FA)
    Mode: Temporary seizure
    Deposit date: 24/02/2021
    Deposit END date: 10/03/2021
    Thesis director: LLOVERAS MUNTANE, POL MARCEL | TAMARIT MUR, JOSE LUIS
    Committee:
         PRESIDENT: VIVES SANTA EULÀLIA, EDUARD
         SECRETARI: MACOVEZ, ROBERTO
         VOCAL: GONZALEZ SILVEIRA, MARTA
    Thesis abstract: Current refrigeration devices, based on vapour-compression cycles, employ refrigerants such as HFCs, which exhibit a global warming potential a thousand times higher than the one produced by CO2,. Furthermore, the increasing middle class, associated with their refrigeration needs, urges for research in new environmentally friendly refrigerant alternatives.Solid-state caloric effects have been proposed as potential alternatives to replace the vapour-compression refrigeration technologies. They may become giant under the cyclic application and removal of an external field which induces changes in entropy and temperature associated with the occurrence of a first-order phase transition. In this work we specifically focus on caloric effects driven by means of hydrostatic pressure (barocaloric effects, BCEs), which allow us to operate with powder compounds, avoiding fatigue upon cycling. Additionally, a wide variety of materials can be used with BC purposes, due to the possibility of working with powdered samples and to the emergence of BCE associated with any transition volume change.In this dissertation we carried out the study of the BC performance of a series of compounds belonging to four different material families: Plastic crystals (PC), hybrid organic-inorganic perovskites (HOIPs), magnetic alloys and a superionic conductor. The election of these materials is not arbitrary, but relies on several features which anticipate good BCEs, such as large transition entropy changes, pressure sensitivity of the transition temperature and small thermal hysteresis. The small hysteresis avoids losses related with the refrigeration cycle and ensures smaller pressures under which reversibility is observed (which at the same time enable smaller applied work to the refrigerant). Finally, other properties must also be taken into account when designing a refrigeration device: Density, thermal conductivity and costs of production. BCEs are determined by means of a combination of quasi-direct and indirect methods. Firstly, we conduct measurements of atmospheric pressure and high-pressure calorimetry (DSC and DTA, respectively), along with experiments of X-ray diffraction and dilatometry. Then, the isobaric entropy curves are constructed, from which by means of curves subtraction the BCEs can be obtained. Additionally, special attention has been put on reversibility, since cyclability is mandatory for a real refrigeration device. Among the family of PC, derivatives from adamantane (1- and 2-adamantanol) and neopentane (neopentylglycol, neopentyl alcohol, pentaglycerine, tris(hydroxymethyl)aminomethane and 2-amino-2-methyl-1,3-propanediol) have been studied. Results for reversible isothermal entropy changes reach colossal values between 300-500 JK-1kg-1 and 150-500 JK-1kg-1 for neopentane and adamantane derivatives, respectively. These values are associated with adiabatic temperature changes among 10-20 K for pressure changes of ~2.5 kbar.The studied HOIPs ([TMA](Mn(N3)3) and [TMA]2(NaFe(N3)6)) exhibit giant values of ~100 J K-1 kg-1 with temperature changes between 15-20 K for pressure changes of ~2 kbar. It is important to highlight the small pressure required in order to obtain reversibility for these compounds, which is about only ~0.1 kbar.Magnetic alloys MnCoGeB0.03, Mn3NiN, Mn3(Zn0.45In0.55)N and Ni50Mn31.5Ti18.5 have been analysed. Nonetheless, only MnCoGeB0.03 and Mn3(Zn0.45In0.55)N show reversibility. They exhibit ~25 J K-1 kg-1 and 4-10 K under pressure changes of ~3 kbar.Finally, AgI, the only superionic conductor studied in this dissertation, reaches ~50 J K-1 kg-1 and ~10 K under pressure changes of 2 kbar. These results become the most outstanding presented in this thesis when normalized by volume.Finally, several figures of merit are presented, in which the studied materials are put into comparison with each other and with other already reported compounds.
  • CIKOJEVI¿, VIKTOR: Ab-initio quantum Monte Carlo study of ultracold atomic mixtures
    Author: CIKOJEVI¿, VIKTOR
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN COMPUTATIONAL AND APPLIED PHYSICS
    Department: Department of Physics (FIS)
    Mode: Change of supervisor
    Deposit date: 26/02/2021
    Deposit END date: 12/03/2021
    Thesis director: BORONAT MEDICO, JORDI | VRANJES MARKIC, LEANDRA
    Committee:
         PRESIDENT: BULJAN, HRVOJE
         SECRETARI: MASSIGNAN, PIETRO ALBERTO
         VOCAL: TARRUELL, LETICIA
    Thesis abstract: The properties of mixtures of Bose-Einstein condensates at T=0 have been investigated using quantum Monte Carlo (QMC) methods and Density Functional Theory (DFT) with the aim of understanding physics beyond the mean-field theory in Bose-Bose mixtures. In particular, quantum liquid droplets with attractive intraspecies and repulsive interspecies attraction were studied, for which we observed significant contributions beyond Lee Huang Yang (LHY) theory that affect the energy, saturation density, and surface tension. The critical atom number in droplets in free space for total number of atoms N between N=30 and N=2000 was obtained. Results of the surface tension for three values of the attractive interspecies interactions are presented. For a homogeneous system, extensive calculations of the equations of state were performed and we report the influence of finite-range effects in beyond-Bogoliubov theory. In systems interacting with a small (large) effective range, we observe repulsive (attractive) beyond-LHY contributions to the energy. For the droplets in a mixture of 39K atoms, which were observed experimentally for the first time, the calculations of equations of state were performed. Combining QMC-built functionals with DFT, the discrepancy in the estimation of critical atom number between the mean-field theory and experimental results was explained by the proper inclusion of the effective range in inter-particle interaction models. The influence of finite-range effects on breathing and quadrupole modes in 39K quantum droplets was investigated. We predicted a significant deviation in the excitation frequencies when entering a more correlated regime. Finally, the phase diagram of repulsive Bose-Bose mixtures in a spherical harmonic trap using Quantum Monte Carlo calculations was studied. Density profiles were obtained reported and we found the occurrence of three phases: separation of condensates in two blobs, fully mixed and shell-separated phase. A comparison with the Gross-Pitaevskii solutions showed a large deviation in the regime of large mass imbalance and strong interactions. We showed the universality in the density profiles with respect to the s-wave scattering length and found numerical evidence for Gross-Pitaevskii scaling present beyond the regime of applicability of Gross-Pitaevskii equations.

DOCTORAL DEGREE IN CONSTRUCTION ENGINEERING

  • ANITORI, GIORGIO: Risk-based highway bridge inspection intervals
    Author: ANITORI, GIORGIO
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN CONSTRUCTION ENGINEERING
    Department: (DECA)
    Mode: Normal
    Deposit date: 25/02/2021
    Deposit END date: 11/03/2021
    Thesis director: CASAS RIUS, JUAN RAMON
    Committee:
         PRESIDENT: RAMOS SCHNEIDER, GONZALO
         SECRETARI: SILVA CARVALHO CAMPOS MATOS, JOSE ANTONIO
         VOCAL: TANNER, PETER
    Thesis abstract: Infrastructure maintenance programs establish schedules for routine inspections of highway bridges with little consideration of their current conditions. The time interval between two inspections is traditionally set based on experience and on engineering judgment. For example, in the US considerable expenditures are incurred to meet the required biennial routine inspection of all bridges many of which may be in good condition. It is therefore of great interest for the engineering community to develop an approach to control inspection schedules of individual bridges and minimize their associated costs using rational criteria that account for the lower risk of postponing the inspection of bridges that are subject to reduced deterioration mechanisms and low traffic loadings. The implementation of such a risk-based approach would go a long way in helping optimize the limited resources available for maintaining the vast highway infrastructure system. The object of this Ph.D. dissertation is to develop a rational approach for determining a risk-based optimum time interval between bridge inspections. The proposed theoretical approach subsequently serves for proposing a simple procedure that is implementable in routine practice by bridge engineers using easily available bridge-specific data.To illustrate the proposed procedure using actual bridge data, the work uses highway data from the state of New York (NYS) in the United States of America (USA) in the form of Weigh-in-Motion (WIM) truck traffic data and bridge records provided through the National Bridge Inventory (NBI) database. These data are used to develop a theoretical framework able to define the capacity of bridges probabilistically and the risk of bridge failure if a bridge¿s inspection is deferred for a limited period of time.The calculations performed in this dissertation based on data collected in the state of New York are limited to simple span composite steel-concrete superstructures that constitute a large proportion of short to medium span bridges in North America. However, the same concepts can be extended to other types of superstructures and other regions of the world as appropriate data become available.The conclusions of this study include the demonstration of the inadequacy of utilizing a standard two-year inspection interval for all bridges. To overcome this problem a simplified procedure is proposed for an easy practical engineers¿ application.

DOCTORAL DEGREE IN GEOTECHNICAL ENGINEERING

  • BARBOZA DE VASCONCELOS, RAMON: A double-porosity formulation for the THM behaviour of bentonite-based materials
    Author: BARBOZA DE VASCONCELOS, RAMON
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN GEOTECHNICAL ENGINEERING
    Department: (DECA)
    Mode: Normal
    Deposit date: 03/03/2021
    Deposit END date: 17/03/2021
    Thesis director: GENS SOLE, ANTONIO | VAUNAT, JEAN
    Committee:
         PRESIDENT: VILLAR GALICIA, MARÍA VICTORIA
         SECRETARI: PRAT CATALAN, PERE
         VOCAL NO PRESENCIAL: LLORET CABOT, MARTI
    Thesis abstract: The thermo-hydro-mechanical (THM) behaviour of expansive clays has been extensively studied in the last decades due to the potential use of bentonites as components of engineered barrier systems (EBS) in deep geological repositories for high-level and long-lived radioactive wastes. Since the early post closure period, the EBS is subjected to changes in temperature, moisture content and stresses due to the coupled THM processes expected to occur in such an environment. The different structural levels found in unsaturated expansive clays requires the use of constitutive models that considers the explicit distinction of these pore-structure levels in their mathematical formulation in order to reproduce the development of the fabric of bentonite materials subjected to the complex THM paths taking place during the lifetime of a nuclear waste repository. A coupled THM formulation that represents the expansive soil as two overlapped but distinct structural media has been developed in the framework of classical and generalized plasticity theories. In such a double-structure approach, the THM behaviour of the expansive soil is characterized by constitutive laws formulated to account for the relevant processes affecting each porous medium and for the interaction mechanisms relating the deformation and the saturation states of the active clay particles to the structural arrangement of the clay aggregates and to the water potential in the larger interconnected pores. In addition, the mechanical response of the porous medium to any THM loading is intrinsically related to the compressibility of the clay minerals. The irreversible changes in the soil fabric are attributed to the loading-collapse (LC) mechanism and to the micro-macro structural coupling (ß-mechanism). Thermal effects are incorporated into the mathematical formulation of the double structure model, which has been implemented in a finite element code (CODE_BRIGHT) able to solve, in a fully coupled way, the system of partial differential equations arising from the governing equations (balance equations). An explicit and robust integration scheme with automatic sub-stepping and error control has been employed to update the stress tensor and the internal (history) variables. The capabilities of the implemented double-porosity model to predict the expected response of expansive clays under isothermal and non-isothermal scenarios have been checked by the performance of constitutive analyses following a number of prescribed THM paths under confined and unconfined conditions. In addition, sensitivity analyses have been carried out in order to verify the dependence of the local expansive response on the initial conditions and on the sequence of load application. Special attention has been placed on the role played by the pore-water mass transfer between the two pore-structure levels in the development of the swelling potential of the expansive porous medium. The performance of the model in reproducing the actual THM behaviour of laboratory-scale tests has also been examined by means of the modelling of the hydration of two heated columns made of granular bentonite materials, selected as potential buffer materials in the construction of engineered barriers. The comparison between the available experimental data and the model results has shown the ability of the current double-porosity formulation to simulate the main observed features of the THM behaviour of the expansive material when subjected to complex loading paths.

DOCTORAL DEGREE IN MATERIALS SCIENCE AND ENGINEERING

  • BESHARATLOO, HOSSEIN: Micromechanical properties of inorganic multiphase materials
    Author: BESHARATLOO, HOSSEIN
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN MATERIALS SCIENCE AND ENGINEERING
    Department: (CEM)
    Mode: Article-based thesis
    Deposit date: 03/03/2021
    Deposit END date: 17/03/2021
    Thesis director: LLANES PITARCH, LUIS MIGUEL | ROA ROVIRA, JOAN JOSEP
    Committee:
         PRESIDENT: RINALDI, ANTONIO
         SECRETARI: JIMENEZ PIQUÉ, EMILIO
         VOCAL: MSAOUBI, RACHID
    Thesis abstract: This thesis is dedicated to understanding the micromechanical properties of multiphase materials which are indispensable in today¿s engineering applications. The mechanical behavior of these materials is dictated by the intrinsic response of each constitutive phase as well as the fashion in which they interact with each other. Therefore, an accurate assessment of both microstructural characteristics and small-scale mechanical properties becomes key for understanding the macroscopic behavior of these materials.Within the above context, the current study is intended to offer a systematic investigation, aiming to assess small-scale mechanical properties of multiphase materials through a protocol based on massive nanoindentation and statistical analysis. It consists of three sequential stages: (1) microstructural characterization, (2) micromechanical evaluation (massive indentation and statistical analysis), (3) correlation between microstructure and mechanical properties using advanced characterization techniques.Microstructural characterization of studied systems was carried out through extensive field emission scanning electron microscopy analysis. This is an essential step for determining testing parameters to be used when implementing massive indentation, particularly penetration depth of performed imprints. Based on the acquired information, massive indentation testing and statistical analysis of experimentally gathered data were implemented to determine the local properties of several unidentified phases. Such data analysis was then complemented by the use of different advanced characterization techniques for deeper inspection of microstructural features. Main goal of this final step was to define the unidentified mechanically distinct phases, based on physically- based correlations between microstructure features and small-scale properties.The proposed and described protocol has been implemented on three different materials: Duplex Stainless Steels (DSS), Polycrystalline cubic Boron Nitride (PcBN) composite and Ti(C,N)-FeNi cermets. They are representative of metal-metal, ceramic- ceramic, and ceramic-metal systems, respectively.Regarding DSS, the influence of the processing route on the local mechanical properties (hardness (H) and elastic modulus (E)) of ¿ and a phases of a DSS was successfully evaluated. Moreover, a novel 2D histogram of hardness and elastic modulus was introduced and validated as an effective tool to correlate microstructure and intrinsic mechanical properties of the constitutive phases of DSSs.PcBN composite consists of cBN particles embedded within a TiN binder. The correlation of relative B/N ratio and local hardness for individual cBN particles was studied, through complementary analysis using electron probe X-ray microanalysis of the data attained using the proposed methodology.The influence of ceramic/metal phase ratio and C addition on the local hardness of Ti(C,N)¿FeNi cermets have been assessed. Regarding the small-scale properties of the constitutive phases, the intrinsic hardness of both Ti(C,N) particles and FeNi binder were determined using the suggested testing procedure.It has been proven that the proposed methodology can be considered as a successful testing protocol for determining small-scale mechanical properties (H and E) of the studied multiphase systems. Nevertheless, successful implementation requires careful consideration of testing parameters used, based on microstructural, residual imprint, and plastic flow length scales.

DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING

  • SARABANDI, SOHEIL: Solving the Nearest Rotation Matrix Problem in Three and Four Dimensions with Applications in Robotics
    Author: SARABANDI, SOHEIL
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN MECHANICAL, FLUIDS AND AEROSPACE ENGINEERING
    Department: Institute of Robotics and Industrial Informatics (IRI)
    Mode: Normal
    Deposit date: 19/02/2021
    Deposit END date: 05/03/2021
    Thesis director: THOMAS ARROYO, FEDERICO
    Committee:
         PRESIDENT: OTTAVIANO, ERIKA
         SECRETARI: ROS GIRALT, LLUIS
         VOCAL: SALTARÉN PAZMIÑO, ROQUE JACINTO
    Thesis abstract: Since the map from quaternions to rotation matrices is a 2-to-1 covering map, this map cannot be smoothly inverted. As a consequence, it is sometimes erroneously assumed that all inversions should necessarily contain singularities that arise in the form of quotients where the divisor can be arbitrarily small. This misconception was clarified when we found a new division-free conversion method. This result triggered the research work presented in this thesis. At first glance, the matrix to quaternion conversion does not seem to be a relevant problem. Actually, most researchers consider it as a well-solved problem whose revision is not likely to provide any new insight in any area of practical interest. Nevertheless, we show in this thesis how solving the nearest rotation matrix problem in Frobenius norm can be reduced to a matrix to quaternion conversion. Many problems, such as hand-eye calibration, camera pose estimation, location recognition, image stitching etc. require finding the nearest proper orthogonal matrix to a given matrix. Thus, the matrix to quaternion conversion becomes of paramount importance. While a rotation in 3D can be represented using a quaternion, a rotation in 4D can be represented using a double quaternion. As a consequence, the computation of the nearest rotation matrix in 4D, using our approach, essentially follow the same steps as in the 3D case. Although the 4D case might seem of theoretical interest only, we show in this thesis its practical relevance thanks to a little known mapping between 3D displacements and 4D rotations. In this thesis we focus our attention in obtaining closed-form solutions, in particular those that only require the four basic arithmetic operations because they can easily be implemented on microcomputers with limited computational resources. Moreover, closed-form methods are preferable for at least two reasons: they provide the most meaningful answer because they permit analyzing the influence of each variable on the result; and their computational cost, in terms of arithmetic operations, is fixed and assessable beforehand. We have actually derived closed-form methods specifically tailored for solving the hand-eye calibration and the pointcloud registration problems which outperform all previous approaches.

DOCTORAL DEGREE IN PHOTONICS

  • PADRÓN BRITO, MARÍA AUXILIADORA: Quantum nonlinear optics at the single-photon level with cold Rydberg atoms
    Author: PADRÓN BRITO, MARÍA AUXILIADORA
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN PHOTONICS
    Department: Institute of Photonic Sciences (ICFO)
    Mode: Normal
    Deposit date: 19/02/2021
    Deposit END date: 05/03/2021
    Thesis director: DE RIEDMATTEN, HUGUES
    Committee:
         PRESIDENT: BROWAEYS, ANTOINE
         SECRETARI: TARRUELL, LETICIA
         VOCAL: HENNRICH, MARKUS THOMAS
    Thesis abstract: Photons are good candidates for carrying quantum information because they are very stable particles: they interact weaklywith the medium and barely with each other. However, this has drawbacks when you want to process the informationbecause, in this case, it is preferable to have photon-photon interactions. For example, for applications in quantum repeaters,such interactions would allow deterministic Bell state measurements, increasing the entanglement distribution rate betweentwo remote nodes. Getting two photons to interact with each other efficiently requires mapping them into a nonlinear mediumat the single-photon level, that is, a medium that reacts differently when it interacts with a single photon than when it doeswith two. Such strong nonlinearity has been demonstrated with Rydberg atoms, which are atoms excited to a state with a highprincipal quantum number.In this thesis we have performed nonlinear quantum optics experiments using an ensemble of cold Rydberg atoms, wherewe have studied the properties of the quantum light emitted by these atoms. First, we demonstrated nonlinearities at thesingle-photon level. To reach this stage, we made several improvements to the previous experimental setup available in thegroup, of which the implementation of a dipole trap was especially relevant. We evidence quantum nonlinearity by measuringphoton antibunching for the transmitted light after interacting with the Rydberg state under electromagnetically inducedtransparency (EIT). We also showed the generation of single photons on-demand after storing weak coherent states of lightpulses as collective Rydberg excitations.Then, we studied the variation of the light statistic throughout the output pulse after propagating through the medium asRydberg polaritons, which are superposition states of light and Rydberg excitations. We showed that the properties at thebeginning and the end of the pulse were different from those of the steady state. In particular, the light detected after the inputpulse was abruptly turned off gave much stronger suppression of two-photon events. Then, we investigated how to exploitthis effect to generate single photons on demand. To do this, we analyzed the quality of the single photons detected at theend of the pulse as a function of the detection probability and compared the results with those obtained by storing the inputpulse as collective Rydberg excitations. We showed that the photons were generated more efficiently when increasing thedetection window at the cost of deteriorating the single photons statistics.Finally, we investigated the indistinguishability of the photons emitted by our Rydberg atomic ensemble, a crucial property forusing Rydberg atoms as nodes in quantum networks. We also compared the single photons generated after storage underEIT conditions with those obtained using a two-photon Raman excitation to the Rydberg state. We measured theindistinguishability by making them interfere with weak coherent states of light in a Hong-Ou-Mandel experiment. And weshowed that, although we obtained better photon statistics under EIT conditions, the indistinguishability from those obtainedwith Raman excitation was significantly higher.
  • PALOMBO BLASCETTA, NICOLA: Deterministic control of nanoantenna and single-photon emitter interaction at the nanoscale
    Author: PALOMBO BLASCETTA, NICOLA
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN PHOTONICS
    Department: Institute of Photonic Sciences (ICFO)
    Mode: Normal
    Deposit date: 24/02/2021
    Deposit END date: 10/03/2021
    Thesis director: VAN HULST, NIEK
    Committee:
         PRESIDENT: TONINELLI, COSTANZA
         SECRETARI: EFETOV, DMITRI K.
         VOCAL: FRIMMER, MARTIN
    Thesis abstract: Deterministic control of nanoantenna and single-photon emitter interaction at the nanoscale220600 220919 221100 220900The study of light-matter interaction at the nanoscale is a very promising field of research, providing the possibility to manipulate theinteraction with single quantum systems like single atoms, molecules, atomic defects or quantum dots, systems that can emit onephoton at a time, so-called single-photon emitters (SPEs). From the fundamental point of view, light-matter interaction at thenanoscale allows the exploration of the ultrasmall, providing superresolution and decomposition of the ensemble. From the appliedpoint of view, it offers the possibility to manipulate SPEs and control their optical properties for important applications in the field ofultrasensitive detectors development and quantum communications.Yet, the ultrasmall SPEs have a relatively small absorption cross-section, making their interaction with light quite weak. In fact, evenin a tight excitation focus at room temperature they only absorb one photon over ten million. Additionally, in many cases suchemitters have a low quantum efficiency, making them hard to detect. Furthermore, in many cases, they are optically quite fragile andtend to blink and bleach, thus no high illumination powers can be used in order to increase their emission of light.Fortunately, nanoantennas allow to confine light well below the diffraction limit, and through efficient coupling can increase theeffective absorption cross-section of SPEs, allowing effective excitation and high-resolution imaging. Moreover, nanoantennascoupled to SPEs modify the local mode density, shortening the emitters excited state lifetime, increasing the internal quantumefficiency, resulting in bright SPEs.In this thesis, we study the interaction of light and matter at the nanoscale through deterministic coupling between a SPE and ananoantenna, using nanometer scale control. We use scanning probe technology to scan a single nanoantenna in close proximityto a single emitter. First, we show a novel near-field probe based on a dipolar nanoantenna design that provides a higher opticaland topographical resolution compared to the state-of-the-art. Next, we apply such novel antenna probes to the study of recentlydiscovered single atomic defects in hBN, ultrastable SPEs in an atomically thin layer, ideal for nanoscale control. Despite the hBNhigh refractive index, and the low absorption cross-section of the defect, we provide high-resolution imaging of single hBN emissioncenters, enhanced by the hot-spot of our antenna probe. The controlled interaction is demonstrated by lifetime mapping, showing ashorter lifetime for the coupled emitter-antenna case. Finally, we develop a novel light confinement mechanism based on localsubwavelength field suppression by near field interference: generating ¿cold¿ spots. We obtain such dark spots by antenna phaseengineering through length control. We image optically for the first time and with high resolution the cold spots, and measurefluorescence lifetime reduction, inhibition of emission for the coupled system, despite the losses of the metallic nanoantenna.Such low-intensity sub-wavelength dark spots provide novel tools for high-resolution imaging of SPEs with ultralow intensity anda nanoscaling of advanced super-resolution techniques like MINFLUX.
  • URGELL FLORES, CARLES: New phenomena in high-quality suspended nanotube devices
    Author: URGELL FLORES, CARLES
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN PHOTONICS
    Department: Institute of Photonic Sciences (ICFO)
    Mode: Normal
    Deposit date: 25/02/2021
    Deposit END date: 11/03/2021
    Thesis director: BACHTOLD, ADRIAN
    Committee:
         PRESIDENT: KONTOS, TAKIS
         SECRETARI: CHANG, DARRICK
         VOCAL: STEELE, GARY
    Thesis abstract: Carbon nanotubes (CNTs) have attracted the attention of the scientific community since their discovery in the 90s. They arean excellent material for the development of research fields as diverse as nanomechanics or quantum transport. Nanotubemechanical resonators are endowed with exceptional properties, including extremely small mass, ultra narrow crosssection,and operation over a large frequency range from 10 kHz to 10 GHz. They are also fantastic sensors of both massadsorption and forces.Its electric transport properties are remarkably the long ballistic transport of charge carriers, strong electron-electroninteraction, and the important role of the spin and valley degrees of freedom. It is possible to observe a wide range ofquantum transport phenomena ranging from single-electron tunneling to Kondo physics and Fabry-Pérot interference. Itshould be noted that the electrical transport and mechanical motion of suspended nanotubes can be coupled by a largeamount.In the first part of this thesis, we present an advanced ultra-sensitive fabrication method that allows us to build andfunctionalize a nanotube cantilever for optical measurements. We grow a platinum particle at the end of the nanotube in orderto increase laser reflection. For this, we track the material deposition on the cantilever through the electromechanicalcoupling with the electron beam during the process.Next, we show electron transport measurements in high-quality devices with high transmission. While high-temperaturemeasurements indicate electron-electron correlations, low-temperature transport characteristics point towards singleparticleFabry-Perot interference. We observe this effect both by modifying the temperature and by tuning the source-drainvoltage. This effect is attributed to the interplay between fluctuations and quantum interactions in a correlated Fabry-Pérotregime.In the last part, we show that it is possible to couple the mechanical movement of the CNT to the electron transport. Byapplying an electron current through the system, we can either cool or amplify the mechanical motion of the eigenmode. Wecooled the nanoresonator down to 4.6+-2.0 quanta of vibration. The instabilities present in electron transport measurementsare attributed to self-oscillation induced by the backaction amplification. These effects have an electrothermal origin. Thismethod can be used in the future to cool NEMS into the quantum regime.

DOCTORAL DEGREE IN SIGNAL THEORY AND COMMUNICATIONS

  • GIRBAU XALABARDER, ANDREU: Sports broadcasting and multiple object tracking with deep learning methods
    Author: GIRBAU XALABARDER, ANDREU
    Thesis file: (contact the Doctoral School to confirm you have a valid doctoral degree and to get the link to the thesis)
    Programme: DOCTORAL DEGREE IN SIGNAL THEORY AND COMMUNICATIONS
    Department: Department of Signal Theory and Communications (TSC)
    Mode: Confidentiality
    Deposit date: 19/02/2021
    Deposit END date: 05/03/2021
    Thesis director: MARQUES ACOSTA, FERNANDO | GIRÓ NIETO, XAVIER | RIUS FERRER, IGNASI
    Committee:
         PRESIDENT: SALGADO ALVAREZ DE SOTOMAYOR, LUIS
         SECRETARI: SALEMBIER CLAIRON, PHILIPPE
         VOCAL: CALDERERO PATINO, FELIPE
    Thesis abstract: Since less than a decade ago, deep learning techniques started to dominate many different fields, revolutionizing the possibilities of artificial intelligence. Seeing their potential, industrial sectors started to invest in applying such technologies as key components of the company strategy. This thesis has been developed in an industrial context, in AutomaticTV. The main focus along this period has been the transfer of knowledge and know-how between academia and industry, development of tools to exploit this knowledge, the exploration of new techniques for future challenges, and, from an academic research perspective, contributions to the multiple object tracking problem.The first part of the thesis is devoted to the introduction of deep learning technologies to AutomaticTV, a company dedicated to automatic sports analysis and broadcasting, and the development of tools and tasks that surround the application.The second part of this thesis introduces the contributions to the multiple object tracking challenge. We present TrajE, a trajectory estimator based on mixture density networks and beam search, used to boost the performance of existing multiple object trackers, and introduce an occlusion reconstruction step using the estimated trajectory information. By adding TrajE to an existing multiple object tracker, we boost its performance by 6.3, 1.8 points in MOTA and IDF1 scores respectively, becoming the new state of the art in the MOTChallenge dataset.

Last update: 05/03/2021 06:03:42.