In textbooks (such as Griffiths, for example), the general method for a solution to the Shrodinger's equation for a single particle, for some V(x), is given as : 1. Get the stationary state solutions 2. Combine them into a linear combination and figure out the coefficients from the known initial state at time 0, ψ(x,0). But it never states how exactly do we know this initial ψ(x,0) in the first place? If we are conducting an experiment with the particle, how do we prepare it to be in exactly the right initial state?