Implementation of generalized quantum measurements for unambiguous discrimination of multiple non-orthogonal coherent states

• Published in: Nature communications Vol. 4; no. 1; p. 2028
• Main Authors: Becerra, F. E., Fan, J., Migdall, A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.06.2013; Nature Publishing Group
• Subjects: 639/766/400/482; Humanities and Social Sciences; Information processing; Measurement techniques; multidisciplinary; Probability; Quantum physics; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms3028

Generalized quantum measurements implemented to allow for measurement outcomes termed inconclusive can perform perfect discrimination of non-orthogonal states, a task which is impossible using only measurements with definitive outcomes. Here we demonstrate such generalized quantum measurements for unambiguous discrimination of four non-orthogonal coherent states and obtain their quantum mechanical description, the positive-operator valued measure. For practical realizations of this positive-operator valued measure, where noise and realistic imperfections prevent perfect unambiguous discrimination, we show that our experimental implementation outperforms any ideal standard-quantum-limited measurement performing the same non-ideal unambiguous state discrimination task for coherent states with low mean photon numbers. Discriminating non-orthogonal quantum states is far from simple due to the inherent measurement difficulties of quantum mechanics. Becerra et al. present a scheme enabling unambiguous discrimination of four non-orthogonal coherent states that outperforms conventional measurements under realistic conditions.