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Chip-integrated visible–telecom entangled photon pair source for quantum communication


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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Fig. 1: Motivation and scheme for a chip-integrated visible–telecom entangled photon pair source.
Fig. 2: Dispersion/coupling engineering essential for the chip-integrated visible–telecom photon source.
Fig. 3: Mode splitting technique is employed to identify the exact mode numbers for phase matching.
Fig. 4: Visible–telecom photon pairs are generated when both phases and frequencies are matched.
Fig. 5: Characterizations show state-of-the-art performance for power efficiency and photon purity.
Fig. 6: Visible–telecom time–energy entanglement is generated and then distributed over distance.

Data availability

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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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.

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Authors and Affiliations



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.

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Correspondence to Xiyuan Lu or Kartik Srinivasan.

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The authors declare no competing interests.

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

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Lu, X., Li, Q., Westly, D.A. et al. Chip-integrated visible–telecom entangled photon pair source for quantum communication. Nat. Phys. 15, 373–381 (2019).

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