Discrepancies between decoherence and the Loschmidt echo

The Loschmidt echo and the purity are two quantities that can provide invaluable information about the evolution of a quantum system. While the Loschmidt echo characterizes instability and sensitivity to perturbations, purity measures the loss of coherence produced by an environment coupled to the system. For classically chaotic systems both quantities display a number of -- supposedly universal -- regimes that can lead on to think of them as equivalent quantities. We study the decay of the Loschmidt echo and the purity for systems with finite dimensional Hilbert space and present numerical evidence of some fundamental differences between them.Comment: 6 pages, 3 figures. Changed title. Added 1 figure. Published version

Multifractality of quantum wave packets

We study a version of the mathematical Ruijsenaars-Schneider model, and reinterpret it physically in order to describe the spreading with time of quantum wave packets in a system where multifractality can be tuned by varying a parameter. We compare different methods to measure the multifractality of wave packets, and identify the best one. We find the multifractality to decrease with time until it reaches an asymptotic limit, different from the mulifractality of eigenvectors, but related to it, as is the rate of the decrease. Our results could guide the study of experimental situations where multifractality is present in quantum systems.Comment: 6 pages, 4 figures, final version including a new figure (figure 1

Decay of the classical Loschmidt echo in integrable systems

We study both analytically and numerically the decay of fidelity of classical motion for integrable systems. We find that the decay can exhibit two qualitatively different behaviors, namely an algebraic decay, that is due to the perturbation of the shape of the tori, or a ballistic decay, that is associated with perturbing the frequencies of the tori. The type of decay depends on initial conditions and on the shape of the perturbation but, for small enough perturbations, not on its size. We demonstrate numerically this general behavior for the cases of the twist map, the rectangular billiard, and the kicked rotor in the almost integrable regime.Comment: 8 pages, 3 figures, revte

Kolmogorov turbulence, Anderson localization and KAM integrability

The conditions for emergence of Kolmogorov turbulence, and related weak wave turbulence, in finite size systems are analyzed by analytical methods and numerical simulations of simple models. The analogy between Kolmogorov energy flow from large to small spacial scales and conductivity in disordered solid state systems is proposed. It is argued that the Anderson localization can stop such an energy flow. The effects of nonlinear wave interactions on such a localization are analyzed. The results obtained for finite size system models show the existence of an effective chaos border between the Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy does not flow to small scales, and developed chaos regime emerging above this border with the Kolmogorov turbulent energy flow from large to small scales.Comment: 8 pages, 6 figs, EPJB style

Informe final del proyecto elaboración y análisis de casos psicosociales por parte del alumnado

Projecte 2014PID-UB/048A continuación se presenta el informe final del proyecto Elaboración y análisis de casos por parte del alumnado (2014PID-UB/048). Mediante este proyecto de dos años de duración se pretendió desarrollar estrategias docentes para fomentar la adquisición de la competencia específica conocer, comprender y analizar el comportamiento por parte de los alumnos de la asignatura Psicología Social del Grado de Psicología de la Universidad de Barcelona. En esta dirección, a lo largo del primer año se planificaron, desarrollaron e implementaron actividades de aprendizaje y de evaluación basadas en la metodología de estudio de casos. A lo largo del segundo año se han realizado modificaciones en las actividades inicialmente planteadas con el fin de mejorar los procesos de aprendizaje del alumnado. Los resultados obtenidos demuestran que la elaboración y el análisis de casos por parte de los estudiantes favorecen su capacidad para comprender y analizar el comportamiento humano. Asimismo, tiene efectos positivos sobre su desempeño en el examen final de la asignatura y sobre su nivel de satisfacción con el curso

Development of psychosocial case studies by students to improve their ability to understand and analyze human behavior

This study presents an active learning methodology based on the development and analysis of case studies by college students and explores its effects on academic performance and on students' capacity of understanding and analysing human behaviour. A group of 54 students who were taking the course Social Psychology at the University of Barcelona developed written stories where psychosocial concepts were represented. Results showed that participants, after developing their own case studies, improved their ability to identify and explain theoretical concepts included in case studies created by the teaching team. The proposed teaching methodology appears to enhance their ability to understand and analyse human behaviour, helping students to integrate theory with reality