His research on the teaching and learning of quantum physics has continued ever since 1995. He was active in the exploration of student misconceptions in the area of quantum physics. He has developed a research-based modern course on quantum mechanics (milq) in which the conceptual issues of quantum mechanics are taught at an introductory level. In the milq project, virtual laboratories - based on computer simulations of the double slit experiment and the Mach-Zehnder interferometer - are used to let the students discover how quantum phenomena deviate from our classical everyday experience. The milq concept has been empirically tested (Müller & Wiesner 2002). The results of the evaluation show that the majority of the students acquired appropriate quantum mechanical conceptions, and that many of the common misconceptions encountered in traditional instruction have been avoided. To supplement the milq course, a comprehensive internet learning platform on the basics of quantum mechanics has been developed ([...][...]). Presently, it consists of a few hundred pages of manuscripts, simulations, and applets. It is visited by several thousand users each month. In Physics Education Research, the milq concept has acquired the status of a gold standard, against which other conceptions are tested. Its elements have been widely adopted in schools and have entered the curriculum recommendations of several German federal states and of the Conference of the Ministers of Education and Cultural Affairs. He will be one of the coordinators for education in the EU Quantum Flagship Project.

Besides his scientific and educational publications, Rainer Müller is the author of well-respected university textbooks on classical mechanics (de Gruyter, 2009) and thermodynamics (de Gruyter, 2013). He is also editor of the renowned high school text book series "Dorn/Bader Physik", which is the market leader in several German federal states.