Roger Yates wrote:‘what language is/can be used to develop these native libraries for QPUs? Is this more assembly-like or are there already compilers for higher level abstractions?’
As you mention per the other Java thread, code to use the libraries can be developed in any language.
To develop the libraries themselves, it depends on whether you're doing...
...or a driver for a physical QPU in which case the language used at the low level of your library may be constrained by specific needs of your hardware, but you can probably still provide high-level interfaces in any languagfe you like.