The probability of occupation of state i {\displaystyle i} is P i ( t ) = | c i ( t ) | 2 = | U i 1 ( t ) | 2 {\displaystyle P_{i}(t)=|c_{i}(t)|^{2}=|U_{i1}(t)|^{2}} . In the case of the starting state, P 1 ( t ) = | c 1 ( t ) | 2 = | U 11 ( t ) | 2 {\displaystyle P_{1}(t)=|c_{1}(t)|^{2}=|U_{11}(t)|^{2}} , and from above, U 11 ( t ) = e − i α t ℏ ( cos ⁡ ( | r | t / ℏ ) − i sin ⁡ ( | r | t / ℏ ) δ | r | ) {\displaystyle U_{11}(t)=e^{\frac {-i\alpha t}{\hbar }}(\cos(|\mathbf {r} |t/\hbar )-i\sin(|\mathbf {r} |t/\hbar ){\frac {\delta }{|\mathbf {r} |}})} . Hence