A Fourier Machine for Quantum Optical Communications

Optical links can achieve spectral efficiencies beyond the Shannon limit by employing quantum joint detection receivers that decode messages collectively. We introduce a novel quantum-enhanced optical system based on Fourier codewords, that are generated and processed by a single arrayed waveguide grating. Numerical comparisons between the Fourier machine and the conventional Green machine demonstrate a quantum advantage in the low photon-number regime for both. Additionally, we propose a parallel configuration of the Fourier machine and numerically investigate its spectral efficiency.