The course is targeted at the advanced undergraduate level and emphasizes formal lectures building on textbook knowledge. This goal meets the requirements of the Les Houches pre-doctoral school program. The course is intended for undergraduates at the European Masters level who are planning a PhD study or PhD students in their first or second year. Young post-docs entering the field can also apply.The aim of the session is to present an introduction to the underlying phenomena. The lectures will present the theoretical basis, the fondamental concepts, the experimental methods, and a few applications.