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Center for Nonlinear Studies |
Small random fluctuations, either of thermal or quantum origin, are the cause of many important and interesting physical phenomena. These include chemical reactions, nucleation in phase transitions (i.e., the formation of a droplet of one phase within another phase), and the formation of unusual spatially localized states in various condensed matter systems. In all of these, random fluctuations (or `noise'), no matter how small, eventually drives a physical system from one stable state to another. We consider both classical and quantum noise. In classical field theories, a crossover between different activation behaviors occurs as one or more control parameters are varied. This crossover has some (but not all) features of a second-order phase transition. This transition shares a number of features with the well-known crossover from thermally activated hopping to quantum tunneling through a barrier as temperature is lowered in certain quantum field theories. We also discuss two timely applications from mesoscopic physics: thermally induced breakup of monovalent metallic nanowires, and stochastic reversal of magnetization in thin ferromagnetic annuli. Each are of interest both from the point of view of fundamental physics and for potential technological applications, some of which will be discussed.
Host: Cristiano Nisoli, T-4/CNLS