Role of degenerate Zeeman states in the storage and retrieval of light pulses

We have studied the role of degenerate Zeeman states in the storage and retrieval of light pulses in the three-level Λ -type system of electromagnetically induced transparency. A probe pulse with the σ+ polarization is stored in the medium and subsequently released with the σ- polarization. However, the manipulation of the retrieved polarization causes an energy loss. Our study shows that the incompatibility between the stored ground-state coherence and the ratio of the probe and coupling Clebsch-Gordan coefficients is responsible for the energy loss. Such energy loss can be avoided as long as all population accumulates in a single Zeeman state. We provide the useful knowledge for the light-storage technique and demonstrate that the degenerate Zeeman states should be considered in the relevant applications.