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Figure 3: (a1-e1) Channel transfer matrices when sending OAM modes , respectively, for different cases. The numbers in (a1-e1) are measured in the quantum domain as the ratio of the measured photon counts to the maximum photon counts in this matrix in a unit of dB. (a2-e2) The photon counts ratio on received OAM modes when sending only OAM photons for different cases. TX: transmitter; RX: receiver.