We report the observation of light storage in a dual memory associated with Zeeman coherence belonging to different hyperfine ground-state levels of cold cesium atoms. This double memory is based on the phenomenon of spontaneous Zeeman coherence transfer as predicted by the tensorial density-matrix formalism describing light interaction with a degenerate two-level system. We employ the two degenerate two-level systems $6S_{1/2},F=4\to 6P_{3/2},F^{\prime }=4$ and $6S_{1/2},F=3\to 6P_{3/2},F^{\prime }=3$, where a coupling beam and a probe beam orthogonally polarized interact resonantly with the first system, inducing Zeeman coherence in both the ground and excited hyperfine levels. The spontaneous Zeeman coherence transfer to the hyperfine ground state of the second system allows for storing the optical information of the probe beam simultaneously in the two hyperfine ground-state levels. Delayed four-wave mixing is employed to demonstrate the observation of the dual memory. Moreover, we also demonstrate the direct optical pumping of Zeeman coherence between the two hyperfine ground states induced by the incident coupling beam, which allows us to increase the storage time of the memory. A theoretical model using a simplified two degenerate two-level system is developed and accounts qualitatively well for the main observed results.

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• Nonlinear optics
• Optical coherence
• Quantum optics