Two-photon processes that involve different sub-levels of the ground state of an atom, are highly sensitive to depopulation and decoherence within the ground state. For example, the spectral width of electromagnetically induced transparency resonance
s in $Lambda-$type system, are strongly affected by the ground state depopulation and decoherence rates. We present a direct measurement of decay rates between hyperfine and Zeeman sub-levels in the ground state of $^{87}$Rb vapor. Similar to the relaxation-in-the-dark technique, pumping lasers are used to pre-align the atomic vapor in a well defined quantum state. The free propagation of the atomic state is monitored using a Ramsey-like method. Coherence times in the range 1-10 ms were measured for room temperature atomic vapor. In the range of the experimental parameters used in this study, the dominant process inducing Zeeman decoherence is the spin-exchange collisions between rubidium atoms.
Reversible and coherent storage of light in atomic medium is a key-stone of future quantum information applications. In this work, arbitrary two-dimensional images are slowed and stored in warm atomic vapor for up to 30 $mu$s, utilizing electromagnet
ically induced transparency. Both the intensity and the phase patterns of the optical field are maintained. The main limitation on the storage resolution and duration is found to be the diffusion of atoms. A techniqueanalogous to phase-shift lithography is employed to diminish the effect of diffusion on the visibility of the reconstructed image.
