Continuous-variable entanglement on a chip



Encoding quantum information in continuous variables, as the quadrature of electromagnetic fields, is a powerful approach to quantum information science and technology1. Continuous-variable entanglement (light beams in Einstein–Podolsky–Rosen, or EPR2, states) is a key resource for quantum information protocols3 and enables hybridization between continuous-variable and single-photon discrete-variable qubit systems4. However, continuous-variable systems are currently limited by their implementation in free-space optical networks, and the demand for increased complexity, low loss, high-precision alignment and stability, as well as hybridization, require an alternative approach. Here we present an integrated photonic implementation of the key capabilities for continuous-variable quantum technologies—the generation and characterization of EPR beams in a photonic chip. When combined with integrated squeezing and non-Gaussian operations, these results will open the way to universal quantum information processing with light.

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Figure 1: Experimental set-up.
Figure 2: On-chip homodyne detection of squeezing.
Figure 3: EPR entanglement verification.


  1. 1

    O'Brien, J. L., Furusawa, A. & Vučković, J. Optical quantum computing. Nature Photon. 3, 687–695 (2009).

    ADS  Article  Google Scholar 

  2. 2

    Einstein, A., Podolsky, B. & Rosen, N. Can quantum-mechanical description of physical reality be considered complete? Phys. Rev. 47, 777–780 (1935).

    ADS  Article  Google Scholar 

  3. 3

    Braunstein, L. & van Loock, P. Quantum information with continuous variables. Rev. Mod. Phys 77, 513–577 (2005).

    ADS  MathSciNet  Article  Google Scholar 

  4. 4

    Furusawa, A. & van Loock, P. Quantum Teleportation and Entanglement: A Hybrid Approach to Optical Quantum Information Processing (Wiley-VCH Verlag, 2011).

    Google Scholar 

  5. 5

    Dowling, J. P. & Milburn, G. J. Quantum technology: the second quantum revolution. Phil. Trans. R. Soc. Lond. A 361, 1655–1674 (2003).

    ADS  MathSciNet  Article  Google Scholar 

  6. 6

    Bouwmeester, D. et al. Experimental quantum teleportation. Nature 390, 575–579 (1997).

    ADS  Article  Google Scholar 

  7. 7

    O'Brien, J. L. Optical quantum computing. Science 318, 1567–1570 (2007).

    ADS  Article  Google Scholar 

  8. 8

    Furusawa, A. et al. Unconditional quantum teleportation. Science 282, 706–709 (1998).

    ADS  Article  Google Scholar 

  9. 9

    Weedbrook, C. et al. Gaussian quantum information. Rev. Mod. Phys. 84, 621–669 (2012).

    ADS  Article  Google Scholar 

  10. 10

    Jeong, H. et al. Generation of hybrid entanglement of light. Nature Photon. 8, 564–569 (2014).

    ADS  Article  Google Scholar 

  11. 11

    Morin, O. et al. Remote creation of hybrid entanglement between particle-like and wave-like optical qubits. Nature Photon. 8, 570–574 (2014).

    ADS  Article  Google Scholar 

  12. 12

    Takeda, S. et al. Deterministic quantum teleportation of photonic quantum bits by a hybrid technique. Nature 500, 315–318 (2013).

    ADS  Article  Google Scholar 

  13. 13

    Politi, A., Cryan, M. J., Rarity, J. G., Yu, S. & O'Brien, J. L. Silica-on-silicon waveguide quantum circuits. Science 320, 646–649 (2008).

    ADS  Article  Google Scholar 

  14. 14

    Matthews, J. C. M., Politi, A., Stefanov, A. & O'Brien, J. L. Manipulation of multiphoton entanglement in waveguide quantum circuits. Nature Photon. 3, 346–350 (2009).

    ADS  Article  Google Scholar 

  15. 15

    Shadbolt, P. J. et al. Generating, manipulating and measuring entanglement and mixture with a reconfigurable photonic circuit. Nature Photon. 6, 45–49 (2012).

    ADS  Article  Google Scholar 

  16. 16

    Laing, A. et al. High-fidelity operation of quantum photonic circuits. Appl. Phys. Lett. 97, 211109 (2010).

    ADS  Article  Google Scholar 

  17. 17

    Duan, L.-M., Giedke, G., Cirac, J. I. & Zoller, P. Inseparability criterion for continuous variable systems. Phys. Rev. Lett. 84, 2722–2725 (2000).

    ADS  Article  Google Scholar 

  18. 18

    Simon, R. Peres–Horodecki separability criterion for continuous variable systems. Phys. Rev. Lett. 84, 2726–2729 (2000).

    ADS  Article  Google Scholar 

  19. 19

    Zhang, T. C., Goh, K. W., Chou, C. W., Lodahl, P. & Kimble, H. J. Quantum teleportation of light field. Phys. Rev. A 67, 033802 (2003).

    ADS  Article  Google Scholar 

  20. 20

    Sprengers, J. P. et al. Waveguide superconducting single-photon detectors for integrated quantum photonic circuits. Appl. Phys. Lett. 99, 181110 (2011).

    ADS  Article  Google Scholar 

  21. 21

    Pernice, W. H. P. et al. High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits. Nature Commun. 3, 1325 (2012).

    ADS  Article  Google Scholar 

  22. 22

    Dakna, M., Anhut, T., Opatrný, T., Knöll, L. & Welsch, D.-G. Generating Schrödinger-cat-like states by means of conditional measurements on a beam splitter. Phys. Rev. A 55, 3184–3194 (1997).

    ADS  Article  Google Scholar 

  23. 23

    Campbell, J. C. Recent advances in telecommunications avalanche photodiodes. J. Lightw. Technol. 25, 109–121 (2007).

    ADS  Article  Google Scholar 

  24. 24

    Takeda, S. et al. Quantum mode filtering of non-Gaussian states for teleportation-based quantum information processing. Phys. Rev. A 85, 053824 (2012).

    ADS  Article  Google Scholar 

  25. 25

    Suzuki, S., Yonezawa, H., Kannari, F., Sasaki, M. & Furusawa, A. 7 dB quadrature squeezing at 860 nm with periodically poled KTiOPO4 . Appl. Phys. Lett. 89, 061116 (2006).

    ADS  Article  Google Scholar 

  26. 26

    Takeno, Y., Yukawa, M., Yonezawa, H. & Furusawa, A. Observation of −9 dB quadrature squeezing with improvement of phase stability in homodyne measurement. Opt. Express 15, 4321–7327 (2007).

    ADS  Article  Google Scholar 

  27. 27

    Masada, G. et al. Efficient generation of highly squeezed light with periodically poled MgO:LiNbO3 . Opt. Express 18, 13114–13121 (2010).

    ADS  Article  Google Scholar 

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The authors thank H. Bachor for advice. This work was partly supported by the Project for Developing Innovation Systems (PDIS), Grants-in-Aid for Scientific Research (GIA) and the Advanced Photon Science Alliance (APSA) commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, the Nippon Telegraph and Telephone Corporation (NTT), the Engineering and Physical Sciences Research Council (EPSRC), the European Research Council (ERC), Photonic Integrated Compound Quantum Encoding (PICQUE), Breaking the Barriers of Optical Integration (BBOI), the US Army Research Office (ARO; grant no. W911NF-14-1-0133) and the US Air Force Office of Scientific Research (AFOSR). J.L.O. acknowledges a Royal Society Wolfson Merit Award and a Royal Academy of Engineering Chair in Emerging Technologies.

Author information




A.F. and J.L.O. planned the project. A.F. supervised the project. G.M. and K.M. conducted the experiment and data analysis. J.L.O. and A.P. developed the waveguide chip. T.H. provided experimental information. G.M., A.P., J.L.O. and A.F. wrote the manuscript with assistance from T.H. and K.M.

Corresponding author

Correspondence to Akira Furusawa.

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The authors declare no competing financial interests.

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Masada, G., Miyata, K., Politi, A. et al. Continuous-variable entanglement on a chip. Nature Photon 9, 316–319 (2015).

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