Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness and high photon purity. However, most quantum systems suitable for local operations, such as storage and computation, support optical transitions in the visible or short near-infrared bands. In comparison to telecommunications wavelengths, the higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fibre-based quantum communication between such local nodes can take place. One approach to connect such systems over fibre is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed in an integrated platform. Here, we demonstrate a nanophotonic visible–telecom photon pair source, using high quality factor silicon nitride resonators to generate narrow-band photon pairs with unprecedented purity and brightness, with a coincidence-to-accidental ratio up to 3,780 ± 140 and a detected photon pair flux up to (18,400 ± 1,000) pairs s−1. We further demonstrate visible–telecom time–energy entanglement and its distribution over a 20 km fibre, far exceeding the fibre length over which purely visible wavelength quantum light sources can be efficiently transmitted. Finally, we show how dispersion engineering of the microresonators enables the connections of different species of trapped atoms/ions, defect centres and quantum dots to the telecommunications bands for future quantum communication systems.

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The data that supports the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

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Journal peer review information: Nature Physics thanks Anthony Laing and other anonymous reviewers for their contribution to the peer review of this work.

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  1. 1.

    Gisin, N. & Thew, R. Quantum communication. Nat. Photon. 1, 165–171 (2007).

  2. 2.

    Lvovsky, A. I., Sanders, B. C. & Tittel, W. Optical quantum memory. Nat. Photon. 3, 706–714 (2009).

  3. 3.

    Simon, C. et al. Quantum memories: A review based on the European integrated project Qubit Applications (QAP). Euro. Phys. J. D 58, 1–22 (2010).

  4. 4.

    Miya, T., Terunuma, Y., Hosaka, T. & Miyashita, T. Ultimate low-loss single-mode fibre at 1.55 μm. Electron. Lett. 15, 106–108 (1979).

  5. 5.

    Raymer, M. G. & Srinivasan, K. Manipulating the color and shape of single photons. Phys. Today 65, 32–37 (2012).

  6. 6.

    Pan, J.-W., Bouwmeester, D., Weinfurter, H. & Zeilinger, A. Experimental entanglement swapping: entangling photons that never interacted. Phys. Rev. Lett. 80, 3891–3894 (1998).

  7. 7.

    Halder, M. et al. Entangling independent photons by time measurement. Nat. Phys. 3, 692–695 (2007).

  8. 8.

    Hensen, B. et al. Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres. Nature 526, 682–686 (2015).

  9. 9.

    Clausen, C. et al. A source of polarization-entangled photon pairs interfacing quantum memories with telecom photons. New J. Phys. 16, 093058 (2014).

  10. 10.

    Söller, C. et al. Bridging visible and telecom wavelengths with a single-mode broadband photon pair source. Phys. Rev. A. 81, 031801 (2010).

  11. 11.

    Schunk, G. et al. Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source. Optica 2, 773–778 (2015).

  12. 12.

    Fekete, J., Rieländer, D., Cristiani, M. & de Riedmatten, H. Ultranarrow-band photon-pair source compatible with solid state quantum memories and telecommunication networks. Phys. Rev. Lett. 110, 220502 (2013).

  13. 13.

    Slattery, O., Ma, L., Kuo, P. & Tang, X. Narrow-linewidth source of greatly non-degenerate photon pairs for quantum repeaters from a short singly resonant cavity. Appl. Phys. B 121, 413–419 (2015).

  14. 14.

    Rieländer, D., Lenhard, A., Mazzera, M. & de Riedmatten, H. Cavity enhanced telecom heralded single photons for spin-wave solid state quantum memories. New J. Phys. 18, 123013 (2016).

  15. 15.

    Caspani, L. et al. Integrated sources of photon quantum states based on nonlinear optics. Light: Sci. Appl. 6, e17100 (2017).

  16. 16.

    Jiang, W. C., Lu, X., Zhang, J., Painter, O. & Lin, Q. Silicon-chip source of bright photon pairs. Opt. Express 23, 20884–20904 (2015).

  17. 17.

    Lu, X., Jiang, W. C., Zhang, J. & Lin, Q. Biphoton statistics of quantum light generated on a silicon chip. ACS Photon. 3, 1626–1636 (2016).

  18. 18.

    Grassani, D. et al. Micrometer-scale integrated silicon source of time–energy entangled photons. Optica 2, 88–94 (2015).

  19. 19.

    Savanier, M., Kumar, R. & Mookherjea, S. Photon pair generation from compact silicon microring resonators using microwatt-level pump powers. Opt. Express 24, 3313–3328 (2016).

  20. 20.

    Ramelow, S. et al. Silicon-nitride platform for narrowband entangled photon generation. Preprint at https://arXiv.org:/abs/1508.04358 (2015).

  21. 21.

    Jaramillo-Villegas, J. A. et al. Persistent energy–time entanglement covering multiple resonances of an on-chip biphoton frequency comb. Optica 4, 655–658 (2017).

  22. 22.

    Wang, J. et al. Multidimensional quantum entanglement with large-scale integrated optics. Science 360, 285–291 (2018).

  23. 23.

    Okawachi, Y. et al. Octave-spanning frequency comb generation in a silicon nitride chip. Opt. Lett. 36, 3398–3400 (2011).

  24. 24.

    Li, Q. et al. Stably accessing octave-spanning microresonator frequency combs in the soliton regime. Optica 4, 193–203 (2017).

  25. 25.

    Karpov, M., Pfeiffer, M. H. P., Liu, J., Lukashchuk, A. & Kippenberg, T. J. Photonic chip-based soliton frequency combs covering the biological imaging window. Nat. Commun. 9, 1146 (2018).

  26. 26.

    Kues, M. et al. On-chip generation of high-dimensional entangled quantum states and their coherent control. Nature 546, 622–626 (2017).

  27. 27.

    Imany, P. et al. 50-GHz-spaced comb of high-dimensional frequency-bin entangled photons from an on-chip silicon nitride microresonator. Opt. Express 26, 1825–1840 (2018).

  28. 28.

    Li, Q., Davanço, M. & Srinivasan, K. Efficient and low-noise single-photon-level frequency conversion interfaces using silicon nanophotonics. Nat. Photon. 10, 406–414 (2016).

  29. 29.

    Boyd, R. W. Nonlinear Optics (Academic Press, Amsterdam, 2008).

  30. 30.

    Agrawal, G. P. Nonlinear Fiber Optics (Academic Press, Amsterdam, 2007).

  31. 31.

    Shah Hosseini, E., Yegnanarayanan, S., Atabaki, A. H., Soltani, M. & Adibi, A. Systematic design and fabrication of high-Q single-mode pulley-coupled planar silicon nitride microdisk resonators at visible wavelengths. Opt. Express 18, 2127–2136 (2010).

  32. 32.

    Lu, X., Rogers, S., Jiang, W. C. & Lin, Q. Selective engineering of cavity resonance for frequency matching in optical parametric processes. Appl. Phys. Lett. 105, 151104 (2014).

  33. 33.

    Inagaki, T., Matsuda, N., Tadanaga, O., Asobe, M. & Takesue, H. Entanglement distribution over 300 km of fiber. Opt. Express 21, 23241–23249 (2013).

  34. 34.

    Sun, Q.-C. et al. Entanglement swapping over 100 km optical fiber with independent entangled photon-pair sources. Optica 4, 1214–1218 (2017).

  35. 35.

    Coimbatore Balram, K. et al. The nanolithography toolbox. J. Res. Natl Inst. Stand. Technol. 121, 464–475 (2016).

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X.L., Q.L., G.M. and A.S. acknowledge support under the Cooperative Research Agreement between the University of Maryland and NIST-CNST, award number 70NANB10H193.

Author information


  1. Microsystems and Nanotechnology Division, Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA

    • Xiyuan Lu
    • , Qing Li
    • , Daron A. Westly
    • , Gregory Moille
    • , Anshuman Singh
    •  & Kartik Srinivasan
  2. Maryland NanoCenter, University of Maryland, College Park, MD, USA

    • Xiyuan Lu
    • , Qing Li
    • , Gregory Moille
    •  & Anshuman Singh
  3. Photon Spot, Inc, Monrovia, CA, USA

    • Vikas Anant


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X.L. led the design, fabrication and measurement of the entangled photon pair source devices. Q.L., A.S., G.M. and K.S. provided assistance with design and measurement. D.A.W. provided assistance with fabrication and V.A. contributed experimental tools. X.L. and K.S. wrote the manuscript. K.S. supervised the project.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Xiyuan Lu or Kartik Srinivasan.

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  1. Supplementary Information

    Supplementary Sections 1–4 and Supplementary Figures 1–4.

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