Experimental demonstration of a scalable M-ary quantum receiver (Conference Presentation)

We report on the first experimental implementation of a scalable M-ary quantum receiver with time-resolved photon detection and real-time adaptive displacement using off-the-shelf components. We implemented M=4, 6, 8, 12, and 16 coherent frequency shift keying communication links with optimal parameters for maximal energy sensitivity. Then, we compared the measured sensitivity with the best sensitivity that can be achieved with a perfect classical measurement (shot noise limit). We observe unconditional, below the shot-noise limit sensitivity and a favorable sensitivity scaling with the alphabet length M.