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Quantum channel capacity for OAM-based free-space optical communications

We study the channel capacity for orbital angular momentum (OAM) based quantum free-space optical communications. Inspired by recent demonstrations for OAM-based single-photon communication, we construct the quantum density operator in matrix form, based on OAM eigenkets, and determine the quantum channel model suitable for study of the quantum communication over atmospheric turbulence channels. The quantum channel model is derived from OAM eigenkets transition probabilities. By using this model we determine the OAM quantum channel capacity in the presence of atmospheric turbulence. The proposed quantum channel model is of high importance for future study of quantum error correction coding to extend the transmission distance and data rate of free-space quantum communications.