  One of the most fascinating aspects of quantum mechanics is the principle
impossibility of deterministic errorless discrimination of nonorthogonal
signals, such as coherent states. On the one hand, it prevents perfect cloning
of quantum states and enables secure communication. On the other hand, it makes
a grand challenge to reach the ultimate measurement precision. Although the
minimum possible error rate (the Helstrom bound) has been known for almost five
decades, there is no practical way to achieve it. Developing the realistic
optimal measurement strategies to attain the Helstrom bound is of utmost
importance for high-precision applications, long-distance free-space and
optical fiber communication, gravitational wave detection, optical sensing in
biology and medicine, to name a few. In this work, we show an optimal receiver
for coherent states which admits a relatively simple technological
implementation. The receiver is based on multichannel splitting of the signal,
followed by feed-forward signal displacement and photon detection.
