Fig. 3: High dimensional state generation.
From: Practical high-dimensional quantum key distribution protocol over deployed multicore fiber
Two replicas of a periodic train of pulse pairs are intensity-modulated at the output of a beam-splitter, prior to transmission in fiber cores A and B, while only the replica in the path to core A is also phase-modulated, so as to generate states in the \({{{{{{{\mathcal{Z}}}}}}}}\) and \({{{{{{{\mathcal{X}}}}}}}}\) bases. An RF signal is used to synchronize modulation in the two spatial paths, where the modulation signals are produced by a field-programmable gate array. Examples of the signals transmitted in two fiber cores are shown in the lower part of the figure, along with the corresponding quantum states.
