Highly efficient storage of 25-dimensional photonic qudit in a cold-atom-based quantum memory

Building an efficient quantum memory in high-dimensional Hilbert spaces is one of the fundamental requirements for establishing high-dimensional quantum repeaters, where it offers many advantages over two-dimensional quantum systems, such as a larger information capacity and enhanced noise resilience. To date, there have been no reports about how to achieve an efficient high-dimensional quantum memory. Here, we experimentally realize a quantum memory that is operational in Hilbert spaces of up to 25 dimensions with a storage efficiency of close to 60%. The proposed approach exploits the spatial-mode-independent interaction between atoms and photons which are encoded in transverse size-invariant orbital angular momentum modes. In particular, our memory features uniform storage efficiency and low cross-talk disturbance for 25 individual spatial modes of photons, thus allowing storing arbitrary qudit states programmed from 25 eigenstates within the high-dimensional Hilbert spaces, and eventually contributing to the storage of a 25-dimensional qudit state. These results would have great prospects for the implementation of long-distance high-dimensional quantum networks and quantum information processing.