On-chip quantum interference between silicon photon-pair sources

Journal name:
Nature Photonics
Year published:
Published online


Large-scale integrated quantum photonic technologies1, 2 will require on-chip integration of identical photon sources with reconfigurable waveguide circuits. Relatively complex quantum circuits have been demonstrated already1, 2, 3, 4, 5, 6, 7, but few studies acknowledge the pressing need to integrate photon sources and waveguide circuits together on-chip8, 9. A key step towards such large-scale quantum technologies is the integration of just two individual photon sources within a waveguide circuit, and the demonstration of high-visibility quantum interference between them. Here, we report a silicon-on-insulator device that combines two four-wave mixing sources in an interferometer with a reconfigurable phase shifter. We configured the device to create and manipulate two-colour (non-degenerate) or same-colour (degenerate) path-entangled or path-unentangled photon pairs. We observed up to 100.0 ± 0.4% visibility quantum interference on-chip, and up to 95 ± 4% off-chip. Our device removes the need for external photon sources, provides a path to increasing the complexity of quantum photonic circuits and is a first step towards fully integrated quantum technologies.

At a glance


  1. Mode of operation, mechanism of photon-pair generation and physical structure of the device.
    Figure 1: Mode of operation, mechanism of photon-pair generation and physical structure of the device.

    a, Schematic of device operation. A bright pump laser is coupled to the SOI chip using a lensed optical fibre and on-chip spot-size converters (not shown). The pump is distributed between two modes via a 2 × 2 MMI coupler (I), and excites the χ(3) SFWM effect within each spiralled SOI waveguide source (II) to produce signal–idler photon pairs in the two-photon entangled state . The pairs are thermo-optically phase shifted (φ, III) and interfered on a second coupler (IV) to yield either bunching or splitting over the two output modes, depending on φ. b, Energy diagrams of both types of SFWM, showing the time-reversal symmetry between the non-degenerate and degenerate processes. c, SOI waveguide cross-section, with the thermal phase shifter on top.

  2. On-chip quantum and classical interference measurements, varying the internal phase [phi].
    Figure 2: On-chip quantum and classical interference measurements, varying the internal phase φ.

    a, Apparatus showing the coupling of light from a bright pump laser into the device via fibre lenses, and the separation of signal (blue), idler (red) and pump (violet) wavelength channels using WDMs. b, Transmission of the bright pump laser shows classical interference. c, Measurement of signal–idler photon splitting between modes A and B, showing quantum interference. d, Measurement of signal–idler photon bunching, with signal and idler both in mode A or mode B. Fringe asymmetry arises from spurious SFWM pairs generated in the I/O waveguides (see text). e, Photon splitting as in b, but with monochromatic photon pairs, created via degenerate SFWM. Coincidence data have accidental coincidences subtracted.

  3. Off-chip HOM quantum interference measurements of [verbar][Psi]split[rang].
    Figure 3: Off-chip HOM quantum interference measurements of |Ψsplitright fence.

    a, Experimental schematic: photon pairs in the |Ψsplitright fence state exit the chip, one is delayed by a displacement x and the other is polarization matched, and then the pair is interfered on a beamsplitter. Two detectors measure coincidences at different signal–idler detunings δ. b, Detuning δ = 9.6 nm. c, Detuning δ = 6.4 nm. d, Detuning δ = 3.2 nm. e. Degenerate SFWM, no detuning. Beating within each fringe is explained by the signal–idler detuning, δ, as plotted in insets to be. Coincidence data have accidental coincidences subtracted. Error bars are Poissonian, based on raw coincidences.


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Author information


  1. Centre for Quantum Photonics, H. H. Wills Physics Laboratory and Department of Electrical and Electronic Engineering, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol BS8 1UB, UK

    • J. W. Silverstone,
    • D. Bonneau,
    • G. D. Marshall,
    • J. G. Rarity,
    • J. L. O'Brien &
    • M. G. Thompson
  2. Corporate Research & Development Center, Toshiba Corporation, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 212-8582, Japan

    • K. Ohira,
    • N. Suzuki,
    • H. Yoshida,
    • N. Iizuka &
    • M. Ezaki
  3. E. L. Ginzton Laboratory, Stanford University, Stanford 94305, USA

    • C. M. Natarajan
  4. School of Engineering, University of Glasgow, James Watt South Building, Glasgow G12 8QQ, UK

    • M. G. Tanner &
    • R. H. Hadfield
  5. Kavli Institute of Nanoscience, TU Delft, Lorentzweg 1, 2628CJ Delft, The Netherlands

    • V. Zwiller


J.W.S. and D.B. contributed equally to this work. J.W.S., D.B., J.G.R., J.L.O'B. and M.G.Th. conceived and designed the experiments. J.W.S., D.B. and M.G.Th. analysed the data. K.O., N.S., H.Y., N.I. and M.E. fabricated the device. R.H.H., V.Z., C.M.N. and M.G.Ta. built the single-photon detector system. J.W.S., D.B. and G.D.M. performed the experiments. J.W.S., D.B., G.D.M., J.G.R., J.L.O'B. and M.G.Th. wrote the manuscript.

Competing financial interests

J.W.S., D.B., J.L.O'B. and M.G.Th. declare UK patent application number 1302895.6.

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