The article mentions switching between "energy states": > This nucleus has two very closely adjacent energy states – so closely adjacent that a laser should in

The article mentions switching between "energy states": > This nucleus has two very closely adjacent energy states – so closely adjacent that a laser should in principle be sufficient to change the state of the atomic nucleus. > the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time. The laser beam had actually switched their state. I don't know enough to explain any further.