Robust Measurement for the Discrimination of Binary Coherent States.

The discrimination of two nonorthogonal states is a fundamental element for secure and efficient communication. Quantum measurements of nonorthogonal coherent states can enhance information transfer beyond the limits of conventional technologies. We demonstrate a strategy for binary state discrimination based on optimized single-shot measurements with photon number resolving detection with a finite number resolution. This strategy enables a high degree of robustness to noise and imperfections while being scalable to high rates and, in principle, allows for surpassing the quantum noise limit (QNL) in practical situations. These features make the strategy inherently compatible with high-bandwidth communication and quantum information applications, providing advantages over the QNL under realistic conditions.