Multimode quantum states with single photons carrying orbital angular momentum.

We propose and experimentally demonstrate a scheme for generating multimode quantum states with single photons carrying orbital angular momentum (OAM). Various quantum states have been realized by superposing multiple OAM modes of single photons in two possible paths. These quantum states exhibit NOON-like "super-resolving" interference behavior for the multiple OAM modes of single photons. Compared with the NOON states using many photons, these states are not only easily prepared, but also robust to photon losses. They may find potential applications in quantum optical communication and recognizing defects or objects. The method to identify a particular kind of defect has been demonstrated both theoretically and experimentally.