Information Theory and Reliable Communication
Information Theory and Reliable Communication
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A simulated photon-number detection via homodyne detectors is considered as a way to improve the efficiency near the single-photon level of communication. Current photon-number detectors at infrared wavelengths are typically characterized by their low detection efficiencies, which significantly reduce the mutual information of a bosonic communication channel. In order to avoid the inefficiency inherent in such direct photon-number detection, we evaluate an alternative set-up based on efficient dual homodyne detection. We show that replacing inefficient direct detectors with homodyne-based simulated direct detectors can yield significant improvements, even near the single-photon level of operation. However we argue that there is a fundamental limit on the ability of homodyne detection to simulate ideal photon number detection, considering the exponential gap between quantum and classical computers. This applies to arbitrarily complicated simulation strategies based on homodyne detection.