This is because, according to the laws of quantum mechanics, it is possible to have transitions between two states, even in the presence of an energy barrier separating the two states, and the phenomenon is called, quite appropriately, quantum tunneling.
なぜなら量子力学の法則によると ２つの状態を隔てる エネルギー障壁があっても その２つの状態の間に — 転移があり得 — その現象を — とても適切な呼び名ですが 量子トンネル現象と呼びます