In the case of a cyclic evolution around a closed path C such that R ( T ) = R ( 0 ) , the closed-path Berry phase is γ γ n = i ∮ ∮ C d R ⟨ ⟨ n ( R ) | ∇ ∇ R | n ( R ) ⟩ ⟩ . An example of physical systems where an electron moves along a closed path is cyclotron motion (details are given in the page of Berry phase). Berry phase must be considered to obtain the correct quantization condition.