Algoritmos cuánticos tolerantes a fallos

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 17-01-2023The framework of this thesis is fault-tolerant quantum algorithms, which can roughly be divided into the following non-disjoint families: a) Grover’s algorithm and quantum walks, b) Shor’s algorithm and hidden subgroup problems, c) quantum simulation algorithms, d) quantum linear algebra, and e) variational quantum algorithms. All of them are covered, to some extent, in this thesis. Grover’s algorithm and quantum walks are described in Chapter 2. We start by highlighting the central role that rotations play in quantum algorithms, explaining Grover’s, why it is optimal, and how it may be extended. Key subroutines explained in this area are amplitude amplification and quantum walks, which will constitute useful parts of other algorithms. In this chapter, we present our Ref. [62], where we explore the heuristic use of quantum Metropolis and quantum walk algorithms for solving anNP-hard problem. This method has been suggested as an avenue to digitally simulate quantum annealing and preparing ground states of many-body Hamiltonians. In the third chapter, in contrast, we turn to the exponential advantages promisedby the Fourier transform in the context of the hidden subgroup problem. However, since this application is restricted to cryptography, we later explore its use in quantum linear algebra problems. Here we explain the development of the original quantum linear solver algorithm, its improvements, and finally the dequantization techniques that would often restrict the quantum advantage to polynomial...El marco conceptual de esta tesis son los algoritmos cuánticos tolerantes a fallos, que pueden dividirse aproximadamente en las siguientes clases no mutuamente excluyentes :a) algoritmo de Grover y paseos cuánticos, b) algoritmo de Shor y problemas de subgrupos ocultos, c) algoritmos de simulación cuántica, d) álgebra lineal cuántica, ye) algoritmos cuánticos variacionales. Todos ellos se tratan, en cierta medida, en esta tesis. El algoritmo de Grover y los paseos cuánticos se explican en el capítulo 2. Comenzamos destacando el papel central que juegan las rotaciones en los algoritmos cuánticos, explicando el de Grover, por qué es óptimo, y cómo puede ser extendido. Las subrutinas clave explicadas en esta área son la amplificación de la amplitud y los paseos cuánticos, que serán partes importantes de otros algoritmos. En este capítulo presentamos nuestra Ref. [62], donde exploramos el uso heurístico de los algoritmos de Metrópolis y paseos cuánticos para resolver problemas NP-difíciles. De hecho, este método ha sido sugerido como una vía para simular digitalmente el método conocido como ‘quantum annealing’,y la preparación de estados fundamentales de Hamiltonianos ‘many-body’.En el tercer capítulo, en cambio, nos centramos en las ventajas exponenciales que promete la transformada de Fourier en el contexto del problema de los subgrupos ocultos. Sin embargo, dado que esta aplicación está restringida a la criptografía, más adelante exploramos su uso en problemas de álgebra lineal cuántica. Aquí explicamos el desarrollo del algoritmo cuántico original para la resolución de sistemas lineales de ecuaciones, sus mejoras, y finalmente las técnicas de ‘descuantización’ que a menudo restringen la ventaja cuántica a polinómica...Fac. de Ciencias FísicasTRUEunpu

QFold: quantum walks and deep learning to solve protein folding

We develop quantum computational tools to predict the 3D structure of proteins, one of the most important problems in current biochemical research. We explain how to combine recent deep learning advances with the well known technique of quantum walks applied to a Metropolis algorithm. The result, QFold, is a fully scalable hybrid quantum algorithm that, in contrast to previous quantum approaches, does not require a lattice model simplification and instead relies on the much more realistic assumption of parameterization in terms of torsion angles of the amino acids. We compare it with its classical analog for different annealing schedules and find a polynomial quantum advantage, and implement a minimal realization of the quantum Metropolis in IBMQ Casablanca quantum system

TFermion: a non-Clifford gate cost assessment library of quantum phase estimation algorithms for quantum chemistry

Quantum Phase Estimation is one of the most useful quantum computing algorithms for quantum chemistry and as such, significant effort has been devoted to designing efficient implementations. In this article, we introduce TFermion, a library designed to estimate the T-gate cost of such algorithms, for an arbitrary molecule. As examples of usage, we estimate the T-gate cost of a few simple molecules and compare the same Taylorization algorithms using Gaussian and plane-wave basis

Initial state preparation for quantum chemistry on quantum computers

Quantum algorithms for ground-state energy estimation of chemical systems require a high-quality initial state. However, initial state preparation is commonly either neglected entirely, or assumed to be solved by a simple product state like Hartree-Fock. Even if a nontrivial state is prepared, strong correlations render ground state overlap inadequate for quality assessment. In this work, we address the initial state preparation problem with an end-to-end algorithm that prepares and quantifies the quality of initial states, accomplishing the latter with a new metric -- the energy distribution. To be able to prepare more complicated initial states, we introduce an implementation technique for states in the form of a sum of Slater determinants that exhibits significantly better scaling than all prior approaches. We also propose low-precision quantum phase estimation (QPE) for further state quality refinement. The complete algorithm is capable of generating high-quality states for energy estimation, and is shown in select cases to lower the overall estimation cost by several orders of magnitude when compared with the best single product state ansatz. More broadly, the energy distribution picture suggests that the goal of QPE should be reinterpreted as generating improvements compared to the energy of the initial state and other classical estimates, which can still be achieved even if QPE does not project directly onto the ground state. Finally, we show how the energy distribution can help in identifying potential quantum advantage

Anti-Spike antibodies 3 months after SARS-CoV-2 mRNA vaccine booster dose in patients on hemodialysis: the prospective SENCOVAC study

Background: Patients on hemodialysis are at high-risk for complications derived from coronavirus disease 2019 (COVID-19). The present analysis evaluated the impact of a booster vaccine dose and breakthrough severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections on humoral immunity 3 months after the booster dose. Methods: This is a multicentric and prospective study assessing immunoglobulin G anti-Spike antibodies 6 and 9 months after initial SARS-CoV-2 vaccination in patients on hemodialysis that had also received a booster dose before the 6-month assessment (early booster) or between the 6- and 9-month assessments (late booster). The impact of breakthrough infections, type of vaccine, time from the booster and clinical variables were assessed. Results: A total of 711 patients [67% male, median age (range) 67 (20-89) years] were included. Of these, 545 (77%) received an early booster and the rest a late booster. At 6 months, 64 (9%) patients had negative anti-Spike antibody titers (3% of early booster and 29% of late booster patients, P =. 001). At 9 months, 91% of patients with 6-month negative response had seroconverted and there were no differences in residual prevalence of negative humoral response between early and late booster patients (0.9% vs 0.6%, P =. 693). During follow-up, 35 patients (5%) developed breakthrough SARS-CoV-2 infection. Antibody titers at 9 months were independently associated with mRNA-1273 booster (P =. 001), lower time from booster (P =. 043) and past breakthrough SARS-CoV-2 infection (P <. 001). Conclusions: In hemodialysis patients, higher titers of anti-Spike antibodies at 9 months were associated with mRNA-1273 booster, lower time from booster and past breakthrough SARS-CoV-2 infectionThe present project has been supported by Fresenius Medical Care, Diaverum, Vifor Pharma, Vircell, Fundación Renal Iñigo Álvarez de Toledo and ISCIII FEDER funds RICORS2040 (RD21/0005

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Conmemoraciones e identidades (trans)nacionales, entre España y América Latina

Las conmemoraciones atraen la atención de la historia cultural de la política, sobre todo a la hora de estudiar los nacionalismos y las identidades nacionales. Fiestas anuales, centenarios y otras variantes conmemorativas permiten el conocimiento de los actores, conflictos y discursos implicados en la construcción de las naciones. Este dossier explora una vertiente hasta ahora casi desconocida de estos procesos, la transnacional, que compromete a fuerzas muy diversas, desde los emigrantes hasta los intelectuales pasando por los diplomáticos o los religiosos, y da lugar a identidades supranacionales en un mundo interconectado. Los artículos aquí reunidos, de especialistas de varios países, analizan en profundidad algunos ejemplos de conmemoraciones transnacionales contemporáneas en España, Europa y América Latina. Les commémorations attirent l’attention sur l’histoire culturelle de la politique, en particulier lorsqu’on étudie les nationalismes et les identités nationales. Les festivals annuels, les centenaires et autres variantes commémoratives permettent de connaître les acteurs, les conflits et les discours impliqués dans la construction des nations. Ce dossier explore un aspect jusqu’ici presque inconnu de ces processus, le transnational, qui implique des forces très diverses, des migrants aux intellectuels, diplomates et religieux, et donne naissance à des identités supranationales dans un monde interconnecté. Les articles réunis ici, rédigés par des spécialistes de différents pays, analysent en profondeur quelques exemples de commémorations transnationales contemporaines en Espagne, en Europe et en Amérique latine. The commemorations draw attention to the cultural history of politics, especially when studying nationalisms and national identities. Annual festivals, centenaries and other commemorative variants allow the knowledge of the actors, conflicts and discourses involved in the construction of nations. This dossier explores a hitherto almost unknown aspect of these processes, the transnational, which involves very diverse forces, from migrants to intellectuals, diplomats and religious, and gives rise to supranational identities in an interconnected world. The articles gathered here, by specialists from various countries, analyze in depth some examples of contemporary transnational commemorations in Spain, Europe and Latin America