This applet illustrates an aspect of quantum physics that is difficult to display and, for many students to understand. The time-dependent properties of states in a time-dependent field are often not well covered in quantum mechanics classes, but are of great importance for understanding measurements of real systems. Radiative transitions of quantum states are clear indications of the discrete nature of bound state energies.
The ability of the user to control the simulated system is important for exploring the physics. By changing the populated states, one can see the different allowed and forbidden transitions. By changing the frequency and amplitude of the oscillating field, one can explore resonance and the important parameters that determine the transitions between states.
The comprehensiveness and flexibility of this applet makes it useful for almost any advanced quantum mechanics course.