<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "Quantum dynamics and universality far from equilibrium"^^ . "The aim of the present thesis is to contribute to a better understanding of the nonequilibrium dynamics of isolated many-body quantum systems, and to develop new theoretical methods for their description. Important questions that will be addressed here concern the emergence of universal behavior far from equilibrium as well as the role of genuine quantum effects on the dynamics.\r\n\r\nIn the first part, we study the far-from-equilibrium universal dynamics of relativistic and nonrelativistic quantum field theories close to a nonthermal fixed point. In this regime, the dynamics is characterized by self-similar scaling and transport of conserved quantities. Using classical-statistical simulations we compute the scaling functions and scaling exponents of different equal-time and unequal-time correlation functions, including statistical as well as spectral components. This analysis is complemented by analytical estimates using a resummed kinetic theory based on a nonperturbative 1/N expansion of the two-particle irreducible (2PI) effective action. Our results shed light on the process of condensate formation, the transport of particles at low momenta, as well as the spectrum of excitations.\r\n\r\nIn the second part, we theoretically and experimentally investigate the relaxation dynamics of an XY dipolar-interacting quantum spin model in an external field, which is realized with ultracold Rydberg atoms. Starting from a fully magnetized initial state, we suddenly switch on the external field and study the subsequent demagnetization dynamics. To disentangle the processes responsible for the relaxation in a closed system, we employ a well-defined hierarchy of theoretical approximations. Our analysis reveals the role of disorder and quantum fluctuations in the dynamics.\r\n\r\nIn the last part, we investigate possible extensions of the classical-statistical or truncated Wigner approximation (TWA) to include quantum effects. Corrections to TWA are added by applying the sampling over initial conditions to a larger set of variables and equations of motion to solve. We consider two different approaches. In the first one, we benchmark a scheme based on BBGKY-type equations by comparing to exact solutions of a spin-boson model relevant for trapped-ion experiments. In the second one, we use 2PI equations instead and compare to exact numerical results of an anharmonic oscillator. Furthermore, we test the potential of the method to capture essential aspects needed for quantum thermalization in a relativistic scalar field theory. Our findings indicate that these methods may be capable of describing thermalization in quantum systems in which both classical fluctuations and genuine quantum effects are important."^^ . "2018" . . . . . . . "Asier"^^ . "Piñeiro Orioli"^^ . "Asier Piñeiro Orioli"^^ . . . . . . "Quantum dynamics and universality far from equilibrium (PDF)"^^ . . . "Thesis_Asier_Pineiro_Orioli.pdf"^^ . . . "Quantum dynamics and universality far from equilibrium (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "Quantum dynamics and universality far from equilibrium (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "Quantum dynamics and universality far from equilibrium (Other)"^^ . . . . . . "preview.jpg"^^ . . . "Quantum dynamics and universality far from equilibrium (Other)"^^ . . . . . . "medium.jpg"^^ . . . "Quantum dynamics and universality far from equilibrium (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #23939 \n\nQuantum dynamics and universality far from equilibrium\n\n" . "text/html" . . . "530 Physik"@de . "530 Physics"@en . .