Hello, I am a Physics undergraduate, currently beginning my third (out of four) year of studies. I have already taken courses about Real and Complex Analysis, Linear Algebra, ODEs and PDEs (for Maths), Classical Mechanics (Lagrangian and Hamiltonian formalism), Electromagnetism, Special Relativity and some other that I think that are irrelevant for my question. I'm having QM courses in the current and the next semester. I open the thread, because I managed to finish one of the courses I normally have in this semester from a previous one, so I have time to study something else instead of that one. Currently, I am thinking the Quantum Computing field about the future. Although, I already know some concepts in QM and Dirac's notation (I can solve excercises), I prefer to finish the QM courses before I deal with quantum comptutation. However, I would like to ask if there is any Mathematics subjects I can study, which would be useful for quantum computing. I also mention that I planned to take a group theory course from the next year, but I cannot do this because it doesn't fit my program, so I have to wait till next year. The only extra course I can now take in my university is Differential Geometry, but from what I read it is not so useful for QC and I do not plan to study General Relativity, at least for now. Another option is to self-study topology, which seems more useful (however self-studying is much harder than taking the course...). Finally, I would appreciate it if the subject was also useful for other other parts of Physics (like QFT), since I am not 100% that I will work on QC (when I enrolled at Physics Dept. I planned to work on Theoretical Physics, since I am far better on this, but now I'd like it more if I worked on something more applied - that's how I thought of QC).