A Mathematical Companion to Quantum Mechanics (Dover Books on Physics)

Have only checked a few things, but just open in any page and marvel at the author’s no nonsense approach. Terse, but says what needs to be said and goes directly to the jugular. Certainly can’t be read like a novel, but you will learn an enormous amount if you put in the effort. Very impressive. One can say the same thing about Sternberg’s similar book on differential geometry with physics applications also published by Dover.

Although I have a graduate degree in physics, much of the material here is densely mathematical and beyond what I learned or read. This is not a text to try to learn QM with, but if the mathematical formulism of QM is your thing, this will be an excellent resource.