Superposition between discrete states of a system is widely considered in the literature, but this system, e.g., a $H$ atom, can also have a continuum in its energy spectrum.
Can the state of a system be in a superposition of an energy level in the discrete part of the spectrum with one level in the continuum part (or with an interval thereof)?
In other words: Can an electron in a $H$ atom be in a superposition of bound to and free from the proton?
