  Quantum enhanced receivers are endowed with resources to achieve higher
sensitivities than conventional technologies. For application in optical
communications, they provide improved discriminatory capabilities for multiple
non-orthogonal quantum states. In this work, we propose and experimentally
demonstrate a new decoding scheme for quadrature phase-shift encoded signals.
Our receiver surpasses the standard quantum limit and outperforms all
previously known non-adaptive detectors at low input powers. Unlike existing
approaches, the receiver only exploits linear optical elements and on-off
photo-detection. This circumvents the requirement for challenging feed-forward
operations that limit communication transmission rates and can be readily
implemented with current technology.
