On the nanoscale transmission of quantum angular momentum

The electromagnetic propagation of angular momentum associated with photon spin has evolved into a subject of much broader remit, following the theoretical and experimental realization of optical beams that can convey quantized orbital angular momentum. The possibility of transmitting such information over nanoscale distances raises numerous issues. For example, it is known that electron spin can be relayed by near-field communication between exciton states in quantum dot assemblies; the question arises, can orbital angular momentum be conveyed in a similar way? There are fundamentally important technicalities surrounding such a prospect, representing potentially serious constraints on the viability of angular momentum transfer between electronically distinct components in structured nanomaterials. To resolve these issues it is necessary to interrogate the detailed form of near-field electromagnetic coupling of the relevant transition multipoles. The emerging results exhibit novel connections between angular momentum content in the near-field. The analysis leads to a conclusion that there are specific limitations on the nanoscale transmission of quantum angular momentum, with challenging implications for quantum optical data transmission.