{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"id":[{"id":"https:\/\/ror.org\/03mb6wj31","id-type":"ROR","asserted-by":"publisher"},{"id":"https:\/\/www.isni.org\/000000041937028X","id-type":"ISNI","asserted-by":"publisher"},{"id":"https:\/\/www.wikidata.org\/entity\/Q1640731","id-type":"wikidata","asserted-by":"publisher"}],"name":"Universitat Polit\u00e8cnica de Catalunya","acronym":["UPC"]}],"indexed":{"date-parts":[[2026,2,10]],"date-time":"2026-02-10T18:12:51Z","timestamp":1770747171392,"version":"3.49.0"},"reference-count":0,"publisher":"Universitat Polit\u00e8cnica de Catalunya","license":[{"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/es\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:p>Physics has two main ambitions: to predict and to understand. Indeed, physics aims for the prediction of all natural phenomena. Prediction entails modeling the correlation between an action, the input, and what is subsequently observed, the output.Understanding, on the other hand, involves developing insightful principles and models that can explain the widest possible varietyof correlations present in nature. Remarkably, advances in both prediction and understanding foster our physical intuition and, as a consequence, novel and powerful applications are discovered. Quantum mechanics is a very successful physical theory both in terms of its predictive power as well as in its wide applicability. Nonetheless and despite many decades of development, we do not yet have a proper physical intuition of quantum phenomena. I believe that improvements in our understanding of quantum theory will yield better, and more innovative, protocols and vice versa.This dissertation aims at advancing our understanding and developing novel protocols. This is done through four approaches. The first one is to study quantum theory within a broad family of theories. In particular, we study quantum theory within the family of locally quantum theories. We found out that the principle that singles out quantum theory out of this family, thus connecting quantum local and nonlocal structure, is dynamical reversibility. This implies that the viability of large scale quantum computing can be based on concrete physical principles that can be experimentally tested at a local level without needing to test millions of qubits simultaneously. The second approach is to study quantum correlations from a black box perspective thus making as few assumptions as possible. The strategy is to study the completeness of quantum predictions by benchmarking them against alternative models. Three main results and applications come out of our study. Firstly, we prove that performing complete amplification of randomness starting from a source of arbitrarily weak randomness - a task that is impossible with classical resources - is indeed possible via nonlocality. This establishes in our opinion the strongest evidence for a truly random event in nature so far. Secondly, we prove that there exist finite events where quantum theory gives predictions as complete as any no-signaling theory can give, showing that the completeness of quantum theory is not an asymptotic property. Finally, we prove that maximally nonlocal theories can never be maximally random while quantum theory can, showing a trade-off between the nonlocality of a theory and its randomness capabilities. We also prove that quantum theory is not unique in this respect. The third approach we follow is to study quantum correlations in scenarios where some parties have a restriction on the available quantum degrees of freedom. The future progress of semi-device-independent quantum information depends crucially on our ability to bound the strength of these correlations. Here we provide a full characterization via a complete hierarchy of sets that approximate the target set from the outside. Each set can be in turn characterized using standard numerical techniques. One application of our work is certifying multidimensional entanglement device-independently.The fourth approach is to confront quantum theory with computer science principles. In particular, we establish two interesting implications for quantum theory results of raising the Church-Turing thesis to the level of postulate. Firstly, we show how different preparations of the same mixed state, indistinguishable according to the quantum postulates, become distinguishable when prepared computably. Secondly, we identify a new loophole for Bell-like experiments: if some parties in a Bell-like experiment use private pseudorandomness to choose their measurement inputs, the computational resources of an eavesdropper have to be limited to observe a proper violation of non locality.<\/jats:p>\n                <jats:p>La f\u00edsica tiene dos finalidades: predecir y comprender. En efecto, la f\u00edsica aspira a poder predecir todos los fen\u00f3menos naturales. Predecir implica modelar correlaciones entre una acci\u00f3n y la reacci\u00f3n subsiguiente.Comprender, implica desarrollar leyes profundas que expliquen la m\u00e1s amplia gama de correlaciones presentes en la naturaleza. Avances tanto en la capacidad de predicci\u00f3n como en nuestra comprensi\u00f3n fomentan la intuici\u00f3n f\u00edsica y, como consecuencia, surgen nuevas y poderosas aplicaciones. La mec\u00e1nica cu\u00e1ntica es una teor\u00eda f\u00edsica de enorme \u00e9xito por su capacidad de predicci\u00f3n y amplia aplicabilidad.Sin embargo, a pesar de d\u00e9cadas de gran desarrollo, no poseemos una intuici\u00f3n f\u00edsica satisfactoria de los fen\u00f3menos cu\u00e1nticos.Creo que mejoras en nuestra comprensi\u00f3n de la teor\u00eda cu\u00e1ntica traer\u00e1n consigo mejores y m\u00e1s innovadores protocolos y vice versa.\u00c9sta tesis doctoral trata simult\u00e1neamente de avanzar nuestra comprensi\u00f3n y de desarrollar nuevos protocolos mediante cuatro enfoques distintos.El primero consiste en estudiar la mec\u00e1nica cu\u00e1ntica como miembro de una familia de teor\u00edas: las teor\u00edas localmente cu\u00e1nticas. Probamos que el principio que selecciona a la mec\u00e1nica cu\u00e1ntica, conectando por tanto la estructura cu\u00e1ntica local y no local, es la reversibilidad de su din\u00e1mica.\u00c9sto implica que la viabilidad de la computaci\u00f3n cu\u00e1ntica a gran escala puede ser estudiada de manera local, comprobando experimentalmente ciertos principios f\u00edsicos. El segundo enfoque consiste en estudiar las correlaciones cu\u00e1nticas desde una perspectiva de 'caja negra', haciendo as\u00ed el m\u00ednimo de asunciones f\u00edsicas. La estrategia consiste en estudiar la completitud de las predicciones cu\u00e1nticas, compar\u00e1ndolas con todos los modelos alternativos. Hemos obtenido tres grandes resultados. Primero, probamos que se puede amplificar completamente la aleatoriedad de una fuente de aleatoriedad arbitrariamente d\u00e9bil.\u00c9sta tarea, imposible mediante recursos puramente cl\u00e1sicos, se vuelve factible gracias a la no localidad. \u00c9sto establece a nuestro parecer la evidencia m\u00e1s fuerte de la existencia de eventos totalmente impredecibles en la naturaleza. Segundo, probamos que existen eventos finitos cuyas predicciones cu\u00e1nticas son tan completas como permite el principio de 'no signaling'. \u00c9sto prueba que la completitud de la mec\u00e1nica cu\u00e1ntica no es una propiedad asint\u00f3tica. Finalmente, probamos que las teor\u00edas m\u00e1ximamente no locales no pueden ser m\u00e1ximamente aleatorias, mientras que la mec\u00e1nica cu\u00e1ntica lo es. \u00c9sto muestra que hay una compensaci\u00f3n entre la no localidad de una teor\u00eda y su capacidad para generar aleatoriedad. Tambi\u00e9n probamos que la mec\u00e1nica cu\u00e1ntica no es \u00fanica en \u00e9ste respecto. En tercer lugar, estudiamos las correlaciones cu\u00e1nticas en escenarios d\u00f3nde algunas partes tienen restricciones en el n\u00famero de grados de libertad cu\u00e1nticos accesibles. \u00c9ste escenario se denomina 'semi-device-independent'. Aqu\u00ed encontramos una caracterizaci\u00f3n completa de \u00e9stas correlaciones mediante una jerarqu\u00eda de conjuntos que aproximan al conjunto buscado desde fuera y que pueden ser caracterizados a su vez mediante t\u00e9cnicas num\u00e9ricas estandar. Un aplicaci\u00f3n de nuestro trabajo es la certificaci\u00f3n de entrelazamiento multidimensional de manera 'device-independent'. El cuarto y \u00faltimo enfoque consiste en enfrentar a la mec\u00e1nica cu\u00e1ntica con principios provenientes de la computaci\u00f3n. En particular, establecemos dos implicaciones para la mec\u00e1nica cu\u00e1ntica de elevar la tesis de Church-Turing al nivel de postulado. Primero, mostramos que diferentes preparaciones de un mismo estado mixto, indistinguibles de acuerdo a los axiomas cu\u00e1nticos, devienen distinguibles cuando son preparados de manera computable. Segundo, identificamos un nuevo 'loophole' en experimentos de Bell: si algunas partes en un experimento de Bell usan pseudo aleatoriedad para escoger sus medidas, los recursos computacionales de un esp\u00eda deben ser limitados a fin de observar verdaderamente la no localidad.<\/jats:p>","DOI":"10.5821\/dissertation-2117-95803","type":"dissertation","created":{"date-parts":[[2023,10,15]],"date-time":"2023-10-15T01:27:55Z","timestamp":1697333275000},"approved":{"date-parts":[[2015,9,23]]},"source":"Crossref","is-referenced-by-count":0,"title":["From quantum foundations to quantum information protocols and back"],"prefix":"10.5821","author":[{"sequence":"additional","affiliation":[]},{"given":"Gonzalo de la","family":"Torre Carazo","sequence":"first","affiliation":[]}],"member":"3865","container-title":[],"original-title":[],"deposited":{"date-parts":[[2026,2,10]],"date-time":"2026-02-10T06:35:28Z","timestamp":1770705328000},"score":1,"resource":{"primary":{"URL":"https:\/\/hdl.handle.net\/2117\/95803"}},"subtitle":[],"editor":[{"given":"Antonio","family":"Ac\u00edn dal Maschio","sequence":"first","affiliation":[]}],"short-title":[],"issued":{"date-parts":[[null]]},"references-count":0,"URL":"https:\/\/doi.org\/10.5821\/dissertation-2117-95803","relation":{},"subject":[]}}