sentences:  A two-level atom is a specific type of two-state system in which the atom can be found in the two possible states.The two possible states are if an electron is found in its ground state or the excited state.In many experiments an atom of lithium is used because it can be closely modeled to a two-level atom as the excited states of the singular electron are separated by large enough energy gaps to significantly reduce the possibility of the electron jumping to a higher excited state.