Equivalent efficiency of a simulated photon-number detector

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Abstract
Homodyne detection is considered as a way to improve the efficiency of communication near the single-photon level. The current lack of commercially available infrared photon-number detectors significantly reduces the mutual information accessible in such a communication channel. We consider simulating direct detection via homodyne detection. We find that our particular simulated direct detection strategy could provide limited improvement in the classical information transfer. However, we argue that homodyne detectors (and a polynomial number of linear optical elements) cannot simulate photocounters arbitrarily well, since otherwise the exponential gap between quantum and classical computers would vanish.