Jonas Larson: Quantum phase transitions in open systems

Among the most important concepts of phase transitions is the one of universality. It says that close to a critical point, physical properties are described by a few parameters that do not depend on microscopic details. This implies that we can sort the possible transition into different 'universality classes'. However, recently it has been shown that phase transitions can also occur in non-equilibrium situations were our quantum system is in contact with some environment - an open quantum system. It is not known if these transitions also can be classified into different classes in the same way.

In this talk I will give some general background to quantum phase transitions, assuming some basic knowledge about quantum mechanics. In order to try to address the question about universality in these systems I will study a toy model, the Landau-Zener problem exposed to an environment. The closed version of the same problem have shown to support universality via what is called the Kibble-Zurek mechanism. This mechanism is now applied to the open Landau-Zener problem and we explore if it predict similar universality property.