Electronics Engineer Doing a Bachelor Thesis in Physics
There are two major issues here: on the one hand there is learning and mastering a topic, on the other hand there is writing a thesis merely.

For the former: quantum mechanics is a very delicate subject that requires a deep understanding of classical physics and analytical mechanics, not to mention mathematical methods as theory of operators on Hilbert spaces and differential equations. Learning quantum mechanics is also about understanding quantum mechanics: it is already difficult for people in the field and it will especially be for whom is from the outside. Moreover, there are different sub-topics areas that you may be involved in, and they may differ from what you have read around (quantum mechanics is not what people think it is). 

You will certainly finish writing your thesis successfully, but that does not mean you will have majored and understood the topic well enough to continue doing research about it. A thesis on quantum mechanics is useful if you want to continue investigating the subject in your further career (as, for example, trying to switch to a master's degree in a more related physics area, like nuclear or solid matter physics, or even theoretical physics). Most depends on what you are planning to do afterwards. If you will continue on the engineering side it is advisable to work on a topic that will get you a job as engineer, eventually, otherwise you are going to end up with a science salad without being expert in either field, neither physics nor electronics, since you could have invested your bachelor thesis time otherwise. 

This said, do apply for it. It is always good to at least have the possibility to decide, rather than regretting not to have applied; in addition, always go for whatever makes you feel passionate.