The next seminar “Modelling of materials – theory, model reduction and efficient numerical methods” will take place on Wednesday from 9:00 in lecture room K3. The talk will be given by Nadine Cetin. Please see the details below.

Speaker: **Nadine Cetin**

Title: **Introduction to Quantum Fluids**

Abstract: Helium is the only known element which remains liquid when it is cooled down. At a certain temperature T Helium undergoes a phase transition and becomes a so—called quantum liquid. In this state it is a treasure box for physicists as it requires bringing together many fields of theoretical physics for its understanding. There exist up to date many models for describing its various fascinating properties like superfluidity or the presence of quantized vortices. The latter are singularities in the fluid at which the rotation of the superfluid velocity v_s does not vanish, although it should be a potential flow according to the models. In this talk the physical properties of superfluid helium will be presented, and the two–fluid model will be introduced, on which all further models are more or less based. Since superfluid Helium is a quantum system, it should be understood on the basis of quantum mechanical principles. This has first been done by L. Landau in 1947 who gave with that a microscopic foundation of the hydrodynamic (macroscopic) equations of superfluid Helium. However, up to now it has not been possible to include the dynamics of quantized vortices from scratch, and hence a complete and fundamental understanding based quantum mechanics seems to be still lacking. After a short recap of the basics of quantum mechanics I will present the questions I will be working on in the upcoming months. These include amongst others: how are the different models related? Is it possible to introduce the dynamics of quantized vortices into the models on the basis of quantum mechanical principles? Is many—body quantum mechanics enough or is a description by full quantum field theory necessary?