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Experimental demonstration of a receiver beating the standard quantum limit for multiple nonorthogonal state discrimination

Nature Photonics volume 7, pages 147–152 (2013)Cite this article

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Abstract

Measurement of the state of a quantum system with inherent quantum uncertainty (noise) approaching the ultimate physical limits is of both technological and fundamental interest. Quantum noise prevents any mutually nonorthogonal quantum states, such as coherent states, from being distinguished with perfect accuracy. Optimized quantum measurements for nonorthogonal coherent states allow, in principle, for state discrimination sensitivities surpassing the standard quantum limit. Realizing quantum receivers that can detect multiple coherent states with sensitivity levels approaching the ultimate quantum limits is fundamental to quantum-enhanced measurements, and can optimize the performance of quantum and classical communications as well as future implementations of quantum technologies. Here, we demonstrate the first quantum receiver that unconditionally discriminates four nonorthogonal coherent states with error probabilities below the standard quantum limit. This receiver achieves error rates four times lower than is possible with any ideal conventional receiver with perfect detection efficiency.

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Figure 1: Discrimination strategy.
Figure 2: Experimental implementation of the quantum receiver.
Figure 3: Phase measurement and preparation.
Figure 4: Experimental error probability.

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Acknowledgements

F.E.B. thanks S. Polyakov and A. Restelli for fruitful discussions about FPGA programming and low-noise electronic design, respectively, and I. Spielman for providing the laser diode at 780 nm.

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Authors and Affiliations

  1. Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, 20899, Maryland, USA

    F. E. Becerra, J. Fan & A. Migdall

  2. Laboratory for Telecommunications Sciences, 8080 Greenmead Drive, College Park, 20740, Maryland, USA

    G. Baumgartner & J. T. Kosloski

  3. Department of Electrical and Computer Engineering, 2410 A.V. Williams Building, University of Maryland, College Park, 20742, Maryland, USA

    J. Goldhar

Authors
  1. F. E. Becerra
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  3. G. Baumgartner
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Contributions

F.E.B. designed the experimental implementation of the receiver, performed the measurements and analysed the experimental results. J.F. and A.M. provided assistance. J.G., J.K. and G.B. conceived the initial theoretical measurement strategy. All authors contributed to writing the manuscript.

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Correspondence to F. E. Becerra.

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The authors declare no competing financial interests.

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Becerra, F., Fan, J., Baumgartner, G. et al. Experimental demonstration of a receiver beating the standard quantum limit for multiple nonorthogonal state discrimination. Nature Photon 7, 147–152 (2013). https://doi.org/10.1038/nphoton.2012.316

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