Experimental demonstration of near-optimal quantum receiver using a superconducting transition edge sensor

Optimal and near-optimal quantum receivers can beat the homodyne limit of discriminating two nonorthogonal coherent states. In particular, the near-optimal receiver proposed by Kennedy is promising for optical communication because of its simple setup. Moreover, Takeoka and Sasaki showed one can further improve the performance of the Kennedy receiver by the optimized displacement operation which was experimentally examined by Wittmann et al. for binary phase shift keyed signals. However, the ideal homodyne limit was not beaten in this experiment because they used a commercially available photon detector based on a silicon avalanche photodiode, which does not have sufficient photon detection efficiency.