Unambiguous identification of coherent states: Searching a quantum database

Journal Article · Wed Aug 15 04:00:00 EDT 2007 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.76.022326· OSTI ID:21011401

Sedlak, Michal ^[1]; Ziman, Mario ^[1]; Pribyla, Ondrej ^[2]; Buzek, Vladimir ^[1]; Hillery, Mark ^[3]

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1. Research Center for Quantum Information, Slovak Academy of Sciences, Dubravska cesta 9, 845 11 Bratislava (Slovakia)
2. Faculty of Science, Masaryk University, Kotlarska 2, 611 37 Brno (Czech Republic)
3. Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10021 (United States)

We consider an unambiguous identification of an unknown coherent state with one of two unknown coherent reference states. Specifically, we consider two modes of an electromagnetic field prepared in unknown coherent states vertical bar {alpha}{sub 1}> and vertical bar {alpha}{sub 2}>, respectively. The third mode is prepared either in the state vertical bar {alpha}{sub 1}> or in the state vertical bar {alpha}{sub 2}>. The task is to identify (unambiguously) which of the two modes are in the same state. We present a scheme consisting of three beam splitters capable to perform this task. Although we do not prove the optimality, we show that the performance of the proposed setup is better than the generalization of the optimal measurement known for a finite-dimensional case. We show that a single beam splitter is capable to perform an unambiguous quantum state comparison for coherent states optimally. Finally, we propose an experimental setup consisting of 2N-1 beam splitters for unambiguous identification among N unknown coherent states. This setup can be considered as a search in a quantum database. The elements of the database are unknown coherent states encoded in different modes of an electromagnetic field. The task is to specify the two modes that are excited in the same, though unknown, coherent state.

• OSTI ID: 21011401
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 2 Vol. 76; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BEAM SPLITTING
BEAMS
COMPARATIVE EVALUATIONS
EIGENSTATES
ELECTROMAGNETIC FIELDS
OPTICS
PERFORMANCE