Pure State without Superposition possible?

[rodsika]

Please give an example of pure state without superposition present, is this possible at all?

 

[Bill_K]

(By "pure state" do you mean eigenstate?) Superposition is such a fundamental feature of quantum mechanics, that no, I don't think what you say is possible. A state which is an eigenstate of one observable will inevitably be a superposition of different eigenstates for some other observable that does not commute with it.

Even a pure plane wave - it can be regarded as a superposition of ingoing and outgoing spherical waves about some origin. Or - the ground state of a particle in a one-dimensional potential well. It is nondegenerate, and so is not a superposition of any other energy eigenstates. However it may be considered as a superposition of eigenstates of some operator that does not commute with E, such as for example the position operator.