I can almost guarantee you that German universities will tell you to apply as a first-year student. “Two years of college” is one of the ways in which applicants from the US can qualify for freshman entrance to a German university. (Others being 1 year of college + a certain SAT score, or the right combination of 4-6 AP exams, to include calculus.)
They may evaluate your transcript for transfer credits after you have been accepted, but I wouldn’t get my hopes up too high. Odds are you’ll essentially start your undergraduate degree from scratch.
A few more things to keep in mind:
- You'll need to be fluent in German to get your undergraduate degree at a German university.
- German universities would not let you double major in two relatively unrelated fields such as physics and neuroscience. Gotta pick one or the other.
- Since neuroscience overlaps with medicine, admission will be extremely competitive. As in, competitive enough that many high school valedictorians won't have grades high enough to qualify. Other biology-related major will be similarly competitive. (I would be happy to elaborate on why that's the case if you're curious.) Physics, on the other hand, is a relatively unpopular major and should be easy to gain admission to.
- German universities don't have a concept of undergraduate research. Undergraduate students are mostly a nuisance to faculty who'd rather be working on research than teaching.
- German culture stresses the importance of university students learning to work independently. Don't expect your instructors to follow a textbook, or to cover everything in class that could be on the exam. It's your responsibility to learn everything on the syllabus.
- Since many students have a hard time adjusting to the "you gotta learn on your own" mentality, drop-out rates are high. Typically about 50% of science majors will drop out or change their major after the first year, and as many as 80% in some departments.
- Applying to an American graduate degree after doing college abroad will put you at a severe disadvantage. One of the reasons is that letters of recommendations count a lot for graduate admissions. You will have a hard time getting meaningful letters since faculty rarely interact with undergraduate students in Germany. If you do get letters, the letter-writers will most likely be unknown to the American professors evaluating your application, and hence carry less weight than letters from trusted colleagues.
- Please also keep in mind that some American universities (public universities in particular) don't accept 3-year Bachelor's degrees from Europe for graduate admissions. Applicants from Europe would be advised to complete a Master's degree in Europe first before applying to graduate school (Master or PhD) in the US.