Off-axis retrieval of orbital angular momentum of light stored in cold   atoms
  We report on the storage of orbital angu- lar momentum (OAM) of light of a Laguerre-Gaussian mode in an ensemble of cold cesium atoms and its re- trieval along an axis different from the incident light beam. We employed a time-delayed four-wave mixing configuration to demonstrate that at small angle (2o), after storage, the retrieved beam carries the same OAM as the one encoded in the input beam. A calculation based on mode decomposition of the retrieved beam over the Laguerre-Gaussian basis is in agreement with the experimental observations done at small angle values. However, the calculation shows that the OAM retrieving would get lost at larger angles, reducing the fidelity of such storing-retrieving process. In addition, we have also observed that by applying an external magnetic field to the atomic ensemble the retrieved OAM presents Larmor oscillations, demonstrating the possibility of its manipulation and off-axis retrieval. 
R. A. de Oliveira, L. Pruvost, P. S. Barbosa, W. S. Martins, S.   Barreiro, D. Felinto, D. Bloch, and J. W. R. Tabosa
quant-ph physics.atom-ph physics.optics