Consider the description of three level Ʌ atom having ground states | g 1 ⟩ ⟩ and | g 2 ⟩ ⟩ (for simplicity suppose that the energies of the ground states are the same) and excited state | e ⟩ ⟩ . Suppose in the beginning the total population is in the ground state | g 1 ⟩ ⟩ . Here the logic for transformation of the population from ground state | g 1 ⟩ ⟩ to | g 2 ⟩ ⟩ is that initially the unpopulated states | g 2 ⟩ ⟩ and | e ⟩ ⟩ couple, afterward superposition of states | g 2 ⟩ ⟩ and | e ⟩ ⟩ couple to the state | g 1 ⟩ ⟩ . Thereby a state is formed that permits the transformation of the population into state | g 2 ⟩ ⟩ without populating the excited state | e ⟩ ⟩ . This process of transforming the population without populating the excited state is called the stimulated Raman adiabatic passage.