If water waves are disturbance of the water medium , the light is electromagnetic waves, and the gravity is space-time waves, then what is the medium in which the quantum waves propagate?
I agree that electromagnetic waves do not need a medium to propagate; however to propagate they do need a (spacetime) metric. I think that the same would be true of quantum waves.
Thus they do not need a medium to propagate in, but nevertheless need a metric to propagate "on".