Author: AGARWAL, HITESH
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: 09/11/2022
Reading date: pending
Reading time: pending
Reading place: pending
Thesis director: KOPPENS, FRANK
Committee:
     PRESIDENT: PRUNERI, VALERIO
     SECRETARI: MUELLER, THOMAS
     VOCAL: STAMPFER, CHRISTOPH
Thesis abstract: Despite the extensive research in the semiconductor industry, Moore¿s law is finally slowing down due to increased complexity. Hence, intense efforts are being carried out to explore hybrid solutions by adding additional functionalities to the existing silicon plat- form to keep up with the growing demand. It is colloquially called as ¿Beyond Moore¿ phase. This thesis is a humble attempt to propose graphene, a single atomic sheet of carbon, as an excellent candidate for the ¿Beyond Moore¿ phase optoelectronic applications. In particular, we demonstrate graphene-based optical interconnects: photodetectors and modulators for data communication applications and broadband infrared sensors for hyperspectral space astronomy. Graphene has the highest room temperature mobility known to us, is complementary metal-oxide semiconductor (CMOS) compatible, and has rich electronic and optoelectronic properties. In the first part of this thesis, we used graphene as an active element with a passive silicon waveguide platform to demonstrate electro-absorption modulators and photodetectors. We developed a novel dielectric combination by integrating 2D material with 3D oxides, which enabled us to build a high-quality clean interface with graphene and high-¿ properties. This helped us to overcome fundamental limitations and demonstrate a high modulation efficiency (~ 2.2 dB/V) and high speed (39 GHz) in the same device, surpassing other CMOS-based modulators. In the case of the photodetector, we demonstrated a photo thermoelectric effect (PTE) based detector with high responsivity (55 mA/W) and a set up limited bandwidth of 40 GHz. In the second part of the thesis, we address the perpetual issue of limited light absorption in graphene by demonstrating the first 3D photoconductor based on decoupled bilayer graphene layers with 2D-like properties. Due to the asymmetric environment experienced by our decoupled bilayer graphene layers, they perceive a strong internal crystal field, which results in an intrinsic bandgap opening. We exploited this bandgap to observe a giant photoconductive photoresponse in a broad wavelength range from 2 to 150 µm. This is the first reported alternative to slow and expensive thermal detectors for broadband operation and could be instrumental for hyperspectral imaging and infrared astronomy, bringing us one step closer to unveiling the secrets of the universe. Finally, we reported a strong photoresponse in the out-of-equilibrium criticality state in graphene superlattices at high bias. We found that the criticality state shifts with a change in temperature or light, resulting in a photoresponse, impersonating transition-edge behaviour, which can be potentially interesting for THz single-photon detection in future.

Author: ABIUSO, PAOLO
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: 08/11/2022
Reading date: 12/12/2022
Reading time: 15:00
Reading place: ICFO - Institut de Ciències Fotòniques. Castelldefels
Thesis director: ACÍN DAL MASCHIO, ANTONIO
Committee:
     PRESIDENT: LEWENSTEIN, MACIEJ
     SECRETARI: NAVASCUES COBO, MIGUEL
     VOCAL: BRUNNER, NICOLAS
Thesis abstract: In this thesis, we study the optimization of operational tasks that involve the manipulation of quantum resources. In most cases, such optimizations are aided by understanding the geometric properties of the physical objects involved. We split our results in a first part concerning Thermodynamics, and a second part concerning Information Theory.In the context of Thermodynamics, we first study the optimization of thermal machines. That is, we look for those periodic control protocols, performed on a quantum working fluid, that maximize figures of merit based on power and efficiency. By making small assumptions on the dynamical regimes (of low-dissipation/slow-driving, or fast-driving), we are able to construct and characterize optimal protocols that are valid for large classes of quantum (and classical) thermal machines.Secondly, we study how to design quantum thermal probes that optimize the precision in temperature estimation when put in contact with a thermal bath. The resulting optimal configurations are simple and physically feasible, and show an Heisenberg-like scaling of the optimal sensitivity.In the context of Information Theory, initially we study how to characterize memory effects (information backflows) in the dynamics of open quantum systems, how to detect them and operationally exploit them.Furthermore, in the subfield of Nonlocality, we study relaxations and generalisation of the canonical Bell scenario, which allow us to bring the realization of nonlocal experiments closer to simple, table-top quantum optics. In particular, by considering nonlocality in quantum networks, we are able to design an experiment which only involves simple passive optics and single-photon entangled states, in which it is possible to certify nonlocality without measurement inputs. Likewise, a different relaxation consists in allowing trusted quantum inputs in a Bell experiment. This permits certifying nonlocality of any entangled state, without trusting the measurement device. We study this measurement-device-independent framework to design simple protocols of entanglement detection for continuous-variable states.The results of the thesis are relevant both from the theoretical point of view and for the efficient realisation of the operational tasks analysed.

Author: GARCIA CALATRAVA, CARLOS
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 COMPUTER ARCHITECTURE
Department: (DAC)
Mode: Normal
Deposit date: 29/09/2022
Reading date: 12/12/2022
Reading time: 15:30
Reading place: FIB_ Sala E101 - Edifici C6 - FIB
Thesis director: CUCCHIETTI TABANIK, FERNANDO MARTÍN | BECERRA FONTAL, YOLANDA
Committee:
     PRESIDENT: CARRETERO PÉREZ, JESÚS
     SECRETARI: GARCÍA VIDAL, JORGE
     VOCAL: RAMON TERRADES, ORIOL
Thesis abstract: The rising interest in extracting value from data has led to a broad proliferation of monitoring infrastructures, most notably composed by sensors, intended to collect this new oil. Thus, gathering data has become fundamental for a great number of applications, such as predictive maintenance techniques or anomaly detection algorithms. However, before data can be refined into insights and knowledge, it has to be efficiently stored and prepared for its later retrieval. While General-purpose database management systems, such as Relational Database Management Systems, have been historically capable of managing a wide range of scenarios, they were found inefficient, or even unsuitable, in handling the Velocity and Volume of nowadays large Infrastructures.Aiming to address the specific challenges of Monitoring Infrastructures, specialized systems like Time-Series Database Management Systems arose, becoming the fastest-growing database category since 2019. However, as each monitoring infrastructure has its own particularities, choosing the best fitting candidate solution became fairly laborious. In consequence, implementing efficient solutions involving Time-Series databases became an arduous task, not only in terms of investing in the most appropriate software and hardware infrastructure, but also in terms of finding expert personnel able to keep track and master those rapidly evolving technologies.In order to mitigate these problems, this research proposes a highly efficient Time-Series database approach for monitoring Infrastructures, aimed at providing the best balance between performance and resource consumption, while enabling its deployment in general purpose document-oriented databases, relieving experts from having to learn yet-another database solution from scratch.More precisely, our research provides the three following main contributions: (1) A foundation data model for time-series data over document-oriented databases, aimed at obtaining the best properties from both schema-full and schema-less approximations. (2) A technique for efficiently integrating several contiguous data models into a single time-series data store, creating a data-flow pattern named Cascading Polyglot Persistence. This technique makes it possible to adapt the database to the nature and progression of time-series data along time, as it is tailored to the expected operations to be performed according to the data aging, empowering further performance while limiting resource consumption. (3) A holistic scalability strategy for time-series databases following Cascading Polyglot Persistence, aimed at further maximizing the benefits of our polyglot approach when deploying it in a cluster fashion. In order to evaluate the performance of our approach, we materialize it on top of MongoDB, the most popular NoSQL database, which further facilitates its adoption. In addition, we benchmark it against two alternative solutions: InfluxDB, the most popular time-series database, and MongoDB itself.Our results show that our approach is able to retrieve historical data up to more than 10 times faster than MongoDB, while also globally outperforming InfluxDB. In addition, it has shown to be able to ingest streams of real-time data two times faster than both MongoDB and InfluxDB, while requesting the same disk space as InfluxDB. Regarding its ad hoc scalability approach, it has shown to greatly reduce the number of needed machines, with respect to traditional approaches, while offering a scalability efficiency up to 85%.These outstanding outcomes pave the way towards NagareDB, our time-series database, aimed at integrating all these approaches, providing them as an out-of-the-box solution.

Author: RODRÍGUEZ ECHARRI, ÁLVARO
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: 26/10/2022
Reading date: 12/12/2022
Reading time: 10:00
Reading place: ICFO- Institut de Ciències Fotòniques
Thesis director: GARCÍA DE ABAJO, JAVIER
Committee:
     PRESIDENT: BUSCH, KURT
     SECRETARI: AIZPURUA IRIAZABAL, JAVIER
     VOCAL: PERTSCH, THOMAS
Thesis abstract: The fundamental science and technological applications of light-matter interactions on nanometer length scales form the field of study known as nanophotonics. Explorations in nanophotonics expand our understanding at the interface between classical and quantum physics, while offering the means to address key societal challenges presented by the information and communication age, particularly concerning the development of light-based technologies that perform faster and more efficiently than their electronic counterparts.Light consists of propagating electromagnetic waves that can be guided, diffracted, or scattered through their interaction with matter. As a wave, light is characterized by its wavelength in free space, with the visible spectrum corresponding to ~400 - 800 nm, while the infrared and ultraviolet regimes of electromagnetic radiation emerge at wavelengths just above and below the visible range, respectively. To control light on the nanoscale, one must overcome the well-known Abbe limit of diffraction that prevents the focusing of light on length scales below the optical wavelength, which can be circumvented by employing optical resonances in materials. In particular, we explore plasmons-the collective oscillations of conduction electrons in metals-as a platform to concentrate electromagnetic energy down to nanometric volumes, enhancing the associated electromagnetic fields and light-matter interactions. Noble metals such as gold, silver, and copper represent the standard choice of material in the study of subwavelength optics and plasmonics, while recent advancements in nanofabrication enable customization of their plasmon resonances. In this thesis, we theoretically explore the interaction of light (comprising the mid-infrared, visible, and UV parts of the electromagnetic spectrum) with noble metal films engineered with atomic-scale precision.The manuscript starts with a comprehensive introduction of plasmons in metallic films, emphasizing the unique features that make these subwavelength optical excitations appealing for implementation in technological applications. We go beyond classical electromagnetism approaches by incorporating semi-classical models to describe the optical response of matter at the atomic level, which involves further complexity. Accordingly, the first and second chapters of the thesis are devoted to the introduction of classical and quantum mechanical descriptions of plasmons in metallic films, respectively. Chapter 3 utilizes these pillars as a foundation to study three aspects of light-matter interactions in metallic thin films at the nanoscale on which we concentrate: surface effects, interaction with electron beams, and heterostructure architectures in which we combine ultra-thin metallic films with two-dimensional materials such as graphene. Once we have analyzed different aspects of the linear properties of the plasmonic response, Chapter 4 focuses on the nonlinear optical behaviour of metal films. The first part describes the intrinsic nonlinear properties of metal films, whereas the second part explores a specific nonlinear phenomenon: two-photon luminescence in gold films. Following up with nonlinear properties but deviating from the use of metallic thin films, we propose in Chapter 5 a path to channel entangled photons encoded in the optical modes of a waveguide and excite them by direct external illumination, leveraging the nonlinear properties of the waveguide and that overcomes involved optical elements commonly used in the generation of entangled photon pairs.Overall, the thesis introduces a quantum mechanical model to understand the plasmonic properties of noble metal films, revealing the benefits of few-atom-thick films for boosting light-matter interaction at the nanoscale. We envision that our findings contribute to broadening the fundamental limits in nonlocal and nonlinear nanophotonics, stimulating the generation of new plasmonic and optoelectronic applications.

Author: SANDOVAL VÁSQUEZ, JUAN CARLOS
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 URBANISM
Department: Department of Architectural Design (PA)
Mode: Normal
Deposit date: 23/09/2022
Reading date: 13/12/2022
Reading time: 14:30
Reading place: ETSAB_ Sala de Graus_ meet.google.com/sua-tzus-siq
Thesis director: SABATE BEL, JOAQUIN | LLOP TORNE, CARLOS JUAN
Committee:
     PRESIDENT: SOTOCA GARCIA, ADOLFO
     SECRETARI: HIGUERAS GARCIA, ESTER
     VOCAL: SALTOS GALARZA, WASHINGTON NAPOLEON
Thesis abstract: This work strives to develop an interpretative reading of the process of configuration of the Amazonian territory of Ecuador, a vast territory with an enormous natural predominance and important biological and cultural diversity. The objective of this thesis is to contribute to the understanding of the construction of this territory, to its relearning of knowledge. The work is based on the idea that the traces in the Amazonian territory show the civilization disputes, the forms of territorial occupation of the indigenous peoples and nationalities have been systematically ignored and underestimated, which have been tried to be changed by imposing other patterns of territorial occupation. Dispersed forms of occupation have been considered a problem that must be corrected by concentrating the population in urban settlements. These logics have remained in tension during the last 500 years in which the particularities of the territory have also produced particular results in the configuration of the Ecuadorian Amazon, a configuration that is currently more drastically marked by new ideas that in practice replicate old habits. In order to understand these processes, the work presents four main chapters. The first one describes a long process of confrontation that began in the 16th century and lasted until the middle of the 20th century, in which a missionary project intends to impose new patterns of territorial occupation on indigenous peoples. The ways of occupying the territory are confronted and, although they are antagonistic, they mutually stimulate each other, concentration and dispersion appear as constants in this process that generally prefigures (not configures) the Amazonian territory we know today. The second chapter explains the existence of an internal colonization project developed by the State, which violently occupied and transformed the region in the second half of the 20th century. In this context, modern Amazonia is configured where the Amazonian cities emerge as a by-product, whose forms show their particularities, as they present their own characteristics as a result of the fusion of the important geographical and natural influences as well as the aftermath of the previous missionary project. The third chapter explains where and how the indigenous population settled, makes a historical approach to their transformations, and explains how these two opposing forms of territorial construction end up complementing each other. The fourth chapter explains the emergence of the "New Amazon" (2007 - 2017), a new regulatory framework and existing economic resources drive several urban projects, which from the State, intend to reverse years of abandonment and poverty, among its objectives is to improve the quality of life of indigenous population and nationalities. However, in practice, the opposite has been done, building projects that obviate the existing specificities, imposing exogenous patterns of territorial occupation that significantly change the ways of living, replicating colonial practices of past centuries. Finally, the work explains, from the ways of inhabiting the territory, how indigenous population continues to face challenges as great as those they faced in colonial times, but also demonstrates their capacity, not only of resistance, but also of adaptation to overcome the challenges.