Reversible storage and manipulation of light pulses with orbital angular momentum

We propose a scheme to realize the storage and retrieval of high-dimensional signal field with orbital angular momentum (OAM) in a double-$\Lambda$ system of cold atoms. By employing two counter-propagating controlling fields, we show that the system exists two shape-preserving dark-state polaritons, which propagate in the opposite direction. We demonstrate that stationary light pulses with OAMs can be generated when both the controlling fields are switched on for retrieving the stored signal field from the atomic spin coherence, and the signal fields with OAMs can be manipulated coherently and all-optically through the active operation of the controlling fields in direction and time. The proposed scheme can easily be extended to the reversible storage and manipulation of multiple signal fields with OAMs. Our work is promising for practical application of information processing with large capacity.