BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69d4b24aeb719 DTSTART:20240912T080000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium and Online (Teams) SUMMARY:ICFO | MARÍA BALANZÓ JUANDÓ CLASS:PUBLIC DESCRIPTION:In the beginning of the last century\, we witnessed a change of paradigm in how physics described the world with the formulation of quant um mechanics. This new theory shook the pillars of science by setting fund amental limits on our ability to describe nature. It was able to explain t he laws that govern physics at the microscopic level\, which could not be explained by means of the existing laws. The behavior at such small scales differs significantly from our daily experience. For instance\, exotic ph enomena such as entanglement or nonlocality are exclusively observed at th e microscale. Entanglement and nonlocal correlations represent two essenti al resources in quantum information processing\, enabling novel tasks that are unattainable within a classical framework.\nThe end of the twentieth century has seen a wave of studies on the fundamental properties of quantu m theory. Nowadays\, as a consequence of these advances in quantum theory and experiments\, various companies are selling devices claimed to perform a quantum information task with no classical analog\, such as quantum ran dom number generators\, prototypes of quantum computers\, or quantum key d istribution devices. Since quantum devices cannot be simulated classically \, it is hard to verify them using only classical resources\, which are th e ones available to the average user. Hence\, a natural question to ask ou rselves is how we can verify the properties and functioning of quantum dev ices in an efficient way.\nIn this context\, device-independent protocols have been developed in quantum information theory over the past decade. Th e main advantage of such protocols is that users do not have to make any a ssumption about the inner workings of their devices\, considering them as black boxes. The security and success of a device-independent protocol rel ies on the observation of nonlocal correlations in a Bell experiment.\nThi s thesis is dedicated to provide tools to achieve the certification of qua ntum information devices or tasks in a device-independent way.\nIn the fir st part of this thesis\, we focus on certifying the security of device-ind ependent quantum key distribution. To this end\, we first study whether Be ll nonlocality is a sufficient condition for security in the most used pro tocols\, proving that there exist nonlocal correlations that are not usefu l for secure device-independent quantum key distribution using these proto cols. Moreover\, we study noisy scenarios\, that is when experimental impe rfections are present\, and derive upper bounds on the two-way and one-way key rates for this kind of protocols.\nIn the second part\, we study self -testing\, which is one of the simplest device-independent protocols. Its goal is to recover quantum states solely from the observed measurement cor relations. In the majority of quantum information processing tasks one nee ds to consider a particular quantum state\, making the certification of qu antum states of great importance in the device-independent paradigm. We pr ove that all multipartite states of qubits can be self-tested. Moreover\, we study self-testing in higher-dimensional systems.\nFinally\, in the thi rd part of this thesis\, we tackle the problem of certification of entangl ement. It is well known that certifying the presence of entanglement in a system is a hard task. The key methods for entanglement detection\, entang lement witnesses and positive maps\, rely on our understanding of the math ematical features of multilinear algebra. By using the fact that any separ able state is one to one related to a matrix inequality\, we port previous ly known results on the entanglement of states with positive partial trans pose into the domain of matrix inequalities\, which also allow us to trans late multilinear positive maps back into entanglement witnesses. This appr oach leads to a unified treatment of a large class of matrix inequalities\ , allowing us to find new inequalities on the basis of advances in entangl ement theory.\n \;\nThursday September 12\, 10:00 h. ICFO Auditorium a nd Online (Teams)\nThesis Director: Prof. Dr. Antonio Ací\;n DTSTAMP:20260407T072914Z END:VEVENT END:VCALENDAR