Electromagnetically-induced transparency has become an important tool to control the optical properties of dense media. However, in a broad class of systems, the interplay between inhomogeneous broadening and the existence of several excited levels m
ay lead to a vanishing transparency. Here, by identifying the underlying physical mechanisms resulting in this effect, we show that transparency can be strongly enhanced. We thereby demonstrate a 5-fold enhancement in a room-temperature vapor of alkali-metal atoms via a specific shaping of the atomic velocity distribution.
Electromagnetically induced transparency (EIT) has mainly been modelled for three-level systems. In particular, a considerable interest has been dedicated to the Lambda-configuration, with two ground states and one excited state. However, in the alka
li-metal atoms, which are commonly used, hyperfine interaction in the excited state introduces several levels which simultaneously participate in the scattering process. When the Doppler broadening is comparable with the hyperfine splitting in the upper state, the three-level Lambda model does not reproduce the experimental results. Here we theoretically investigate the EIT in a hot vapor of alkali-metal atoms and demonstrate that it can be strongly reduced due to the presence of multiple excited levels. Given this model, we also show that a well-designed optical pumping enables to significantly recover the transparency.
We consider the coherent stimulated Raman process developing in an optically dense and disordered atomic medium in application to the quantum memory scheme. Our theoretical model predicts that the hyperfine interaction in the excited state of alkali
atoms can positively affect on the quantum memory efficiency. Based on the concept of the coherent information transfer we analyze and compare the memory requirements for storage of single photon and macroscopic multi-photon light pulses.
We consider the coherent stimulated Raman process developing in an optically dense disordered atomic medium, which can also incoherently scatter the light over all outward directions. The Raman process is discussed in the context of a quantum memory
scheme and we point out the difference in its physical nature from a similar but not identical protocol based on the effect of electromagnetically induced transparency (EIT). We show that the Raman and EIT memory schemes do not compete but complement one another and each of them has certain advantages in the area of its applicability. We include in our consideration an analysis of the transient processes associated with switching the control pulse off or on and follow how they modify the probe pulse dynamics on the retrieval stage of the memory protocol.
