  The impossibility of perfectly discriminating non orthogonal quantum states
imposes far-reaching consequences both on quantum and classical communication
schemes. We propose and numerically analyze an optimized quantum receiver for
the discrimination of phase encoded signals. Our scheme outperforms the
standard quantum limit and approaches the Helstrom bound for any signal power.
The discrimination is performed via an optimized, feedback-mediated
displacement prior to a photon counting detector. We provide a detailed
analysis of the influence of excess noise and technical imperfections on the
average error probability. The results demonstrate the receiver's robustness
and show that it can outperform any classical receiver over a wide range of
realistic parameters.
