Orbital angular momentum in quantum information and computation

Light has a long tradition in serving as a model representation for quantum communication systems. Its polarization provides two orthogonal states, for example, horizontal, and vertical, which can be used to encode one bit of information in a quantum system (say, horizontal represents 0 and vertical represents 1). The system does not necessarily need to be horizontally or vertically polarized; it could be left or right circularly polarized or linearly polarized at some other angle. This allows the system to be in a superposition of the orthogonal bit states and therefore to represent what is known as a qubit. Various alternative physical qubit systems are competing in the run toward other feasible quantum information applications, including cold trapped
ions, Bose condensates, and quantum dots. Polarized light, however, is particularly
suitable for proof of principle investigations, as its generation, manipulation, and detection is comparatively simple, fast, and inexpensive. The field is advancing rapidly,
and quantum key distribution has already entered the public domain.