“…The ultimate information rates for such channels, known as classical channel capacities, have been studied extensively in the literature [4]- [6]. However, even though the optimal ensembles of quantum states saturating the classical capacity bound for Gaussian channels have been discovered, the necessary measurement schemes remain largely unknown, with the exception of a few particular scenarios [7]- [9]. These involve regimes of very weak and very strong signal strengths, quantified by the average number of photons per channel use received at the output, in which respectively a photon number resolving (PNR) or a heterodyne detection become almost optimal [4], [7], [8].…”