Stimulated Raman adiabatic passage

Consider the description of three level Ʌ atom having ground states ${\displaystyle |g_{1}\rangle }$ and ${\displaystyle |g_{2}\rangle }$ (for simplicity suppose that the energies of the ground states are the same) and excited state ${\displaystyle |e\rangle }$. Suppose in the beginning the total population is in the ground state ${\displaystyle |g_{1}\rangle }$. Here the logic for transformation of the population from ground state ${\displaystyle |g_{1}\rangle }$ to ${\displaystyle |g_{2}\rangle }$ is that initially the unpopulated states ${\displaystyle |g_{2}\rangle }$ and ${\displaystyle |e\rangle }$ couple, afterward superposition of states ${\displaystyle |g_{2}\rangle }$ and ${\displaystyle |e\rangle }$ couple to the state ${\displaystyle |g_{1}\rangle }$. Thereby a state is formed that permits the transformation of the population into state ${\displaystyle |g_{2}\rangle }$ without populating the excited state ${\displaystyle |e\rangle }$. This process of transforming the population without populating the excited state is called the stimulated Raman adiabatic passage.[5]