In the special case where the system is known to be in an eigenstate of ˆH0, say |k⟩, at t=0, then ck(0)=1 and all other cm(0)=0, m≠k, giving Thus a s...In the special case where the system is known to be in an eigenstate of ˆH0, say |k⟩, at t=0, then ck(0)=1 and all other cm(0)=0, m≠k, giving Thus a system starting in a known eigenstate of the unperturbed system may transform to a different eigenstate through the action of the perturbing potential. The probability of finding the system at a later time, t, in the state |m⟩ where m≠k is given by
