# Interview

If you are have received the invitation to the interview, here are some hints. The most important: You cannot prepare for the interview. That does not mean that we will not discuss physics and mathematics. But we will try to evaluate your ability to solve physics and mathematics problems rather than simply test your knowledge of facts. We would like to see you employing your background and concepts rather than reciting answers for questions you have seen many times before. In short, we want to see you act as a physicist or a mathematician. This is not something you can learn in the few days from the invitation to the interview. So, don't panic and relax!

Our questions can be answered with solid undergraduate knowledge of theoretical physics (mechanics, electrodynamics, quantum mechanics and statistical physics) and mathematics (in particular analysis and linear algebra).To give you a few examples:

- You should know the time independent Schroedinger equation Hf=Ef (for a wave function f) and you should know what you are solving this equation for (what is the unknown(s)). But you are not required to know the exact form of the eigenfunctions (maybe except for the free particle).
- We will not expect you to know the exact formula for the energy levels of the hydrogen atom in terms of the electron mass, the speed of light, Planck's constant etc off the top of your head. But you should know that there are discrete levels that approach 0 from below (ideally you know that they scale like 1/n
^{2}). - You should know how to compute a partition function. But we do not expect you can derive the phase transition for Bose-Einstein condensation at any level of rigor.
- You don't need to know the detailed definition of the Lebesque measure. But you should know that it differs from the Riemann integral (e.g. know an example of a function that can be integrated with one but not the other).
- You should know that an infinite dimensional vector space has an infinite number of linearly independent vectors. But we do to require you to be able to recite a proof that it has a basis.
- If as part of your undergraduate education you have writen some sort of bachelor thesis, we might ask you to summarise it in a few sentences.

The interview typically takes about 30 minutes but this varies. Furthermore, we adopt our questions to your answers. We want to find the boundary of what you can answer. So there is no need to worry if you find that we ask you questions that you cannot answer immediately. We are probably just asking very hard questions. Furthermore, we want to watch you while you solve problems. So there is not much point in asking you things you just know. Rather we want to see you approach a solution. Of course, this might be harder than usual as you might be a bit excited in an interview situation but we try to take this into account. Just be yourself.