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Robust and high-sensitivity nonorthogonal coherent state discrimination

Francisco Elohim Becerra, University of New Mexico

(Session 3 : Thursday from 2:15pm - 2:45pm)

Measurements for accessing the information contained in quantum states are limited by the inherent noise of these states. Strategies for nonorthogonal state discrimination for optimally extracting information from these states have fundamental interest in quantum mechanics and can allow for communications approaching the quantum limits. Conventional measurements for nonorthogonal state discrimination of coherent states with different phases implement a direct phase-sensitive detection, and can ideally reach the standard quantum limit (SQL). However, measurement strategies based on the quantum properties of these states can allow for better measurements which surpass the SQL and approach the ultimate measurement limits allowed by quantum mechanics. We present the demonstration of a receiver based on adaptive measurements and single-photon counting that unconditionally discriminates multiple nonorthogonal coherent states below the SQL. We also discuss the potential of photon-number-resolving detection to provide robustness under realistic conditions for an adaptive coherent receiver with detectors with finite photon-number resolution.