Quantum spin chains

Abstract

Since the introduction of the Heisenberg model to describe the dynamics of localized spins, quantum chains become useful tools for the appropriate understanding of the fluctuations in several physical systems. The quantum chains emerge in three interconnected topics of physics and mathematical physics, that we split in: a) Exactly integrable quantum chains - where they describe the simple evolution operators we can formulate for several interacting many body system; b) Critical phenomena and the thermodynamic properties of general quantum chains - where they usually describe the quantum fluctuations at the temperature T = 0 or/and thermal ones at T 8= 0, and c) Stochastic models - where they describe the time fluctuations in asymptotic equilibrium and non-equilibrium states. On this FAPESP project, in continuation with the last ones, we are going to study quantum chains along the above three topics. In topic a) we are going to search for new exactly integrable chains by using the Matrix Product ansatz introduced in a previous FAPESP project. In topic b) we are going to study the entanglement properties of quantum critical chains, through the calculation of the von Neumann and Rényi entanglement entropies among subsets of the entire quantum chain. We also will study the Shannon mutual information among theses subsets, since from results obtained along the previous FAPESP project, this quantity exhibits an universal behavior that characterizes the critical behavior of the quantum chain. We also will study the disorder effects in several quantum chains, by studying thermodynamic and information quantities. In topic c) we are going to introduce new models, as well to generalize several known models in order to understand which are the necessary basic ingredients that produce a space-time conformal invariance in a non-equilibrium asymptotic state. Within this topic we are going to study the disorder effects in unidimensional contact processes, where there exist a conexion with experimental results. (AU)