Storage of orbital angular momenta of light via coherent population oscillation.

We report on the storage of orbital angular momenta (OAM) of light via the phenomenon of coherent population oscillation (CPO) in cold cesium atoms. The experiment is performed using a delayed four wave mixing configuration, where the transverse optical information of a probe field carrying OAM associated with its azimuthal phase dependence is stored in the CPO of Zeeman sublevels of the hyperfine transition F=3→F'=2 of the cesium D2 line. We also demonstrate experimentally the simultaneous storage and retrieval of different OAM states propagating along different directions in space, leading to algebraic operations with OAM and, therefore, opening the possibility of multiplexing OAM states.