Most quantum mechanics theory out there is taught by physicists.
You'll discover that their brain works in a way that's fundamentally different than that of a computer scientist, making it really hard.
Very specifically, you'll find that they are basically incapable to reason without physical support and/or experiments and sticking to a theoretical presentation of the subject from first principles is not something they can materially do.
Even Scott Aaronson, who claims to try to explay QM and QC using only math falls back to talking about particles and spin and shit after the fourth paragraph.
My recommendation: if you want to learn QM from first mathematical principles, avoid like the plague anything written by a physicist: they're all parroting each other tracing all the way back to Dirac and Bohr.
If you find a book that can talk about QM without using the following words "double slit experiment", "hydrogen atom", "spectrum", "spin", "wave", and only use terms taken from linear algebra in infinite dimensions then you stand a chance to understand.