Stimulated Raman adiabatic passage

The Stimulated Raman adiabatic passage (STIRAP) process permits transfer of a population between two applicable quantum states via at least two coherent electromagnetic (light) pulses. These light pulses drive the transitions of the three level Ʌ atom or multilevel system.^[1][2] The process is a form of state-to-state coherent control.

Population transfer in three level Ʌ atom

Consider the description of three level Ʌ atom having ground states $|g_{1}\rangle$ and $|g_{2}\rangle$ (for simplicity suppose that the energies of the ground states are the same) and excited state $|e\rangle$. Suppose in the beginning the total population is in the ground state $|g_{1}\rangle$. Here the logic for transformation of the population from ground state $|g_{1}\rangle$ to $|g_{2}\rangle$ is that initially the unpopulated states $|g_{2}\rangle$ and $|e\rangle$ couple, afterward superposition of state $|g_{2}\rangle$ and $|e\rangle$ couple to the state $|g_{1}\rangle$. Thereby a state is formed that permits the transformation of the population into state $|g_{2}\rangle$ without populating the excited state $|e\rangle$. This process of transforming the population without populating the excited state is called the stimulated Raman adiabatic passage.^[3]

References

1. Unanyan, R., M. Fleischhauer, B. W. Shore, and K. Bergmann. "Robust creation and phase-sensitive probing of superposition states via stimulated Raman adiabatic passage (STIRAP) with degenerate dark states." Optics communications 155, no. 1 (1998): 144-154.
2. Schwager, Heike (2008). A quantum memory for light in nuclear spin of quantum dot (PDF). Max-Planck-Institute of Quantum Optics.
3. P. Marte, P. Zoller, J.L.Hall. "Coherent atomic mirrors and beam splitters by adiabatic passage in multilevel systems, Phys. Rev A44 , 1991".