The black body remains the most prominent source of light for absolute radiometry1. Its main alternative, synchrotron radiation, requires costly and large facilities2. Quantum optics offers a new radiometric source: parametric down-conversion (PDC), a nonlinear optical process, in which pairwise photon correlations enable absolute calibration of photodetectors3,4,5,6. Since the emission rate crucially depends on the brightness of the electromagnetic field, quantum-mechanical fluctuations of the vacuum7 can be seen as a seed of spontaneous PDC, and their amplitude is a natural radiometric standard. Thus, they allow for the calibration of the spectral radiance of light sources8,9,10,11 by measuring the ratio between seeded and unseeded PDC. Here, we directly use the frequency spectrum of the electromagnetic vacuum to trigger spontaneous PDC and employ the generated light to infer the spectral response of a spectrometer over a broad spectral range. Then, we deduce the absolute quantum efficiency from the spectral shape of PDC in the high-gain regime, without relying on a seed or reference detector. Our results compare well with the ones obtained with a reference lamp, demonstrating a promising primary radiation standard.

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We thank O. Reshef for valuable discussions. This research was performed as part of a collaboration within the Max Planck-University of Ottawa Centre for Extreme and Quantum Photonics, whose support we gratefully acknowledge. This work was supported by the Canada First Research Excellence Fund award on Transformative Quantum Technologies and by the Natural Sciences and Engineering Council of Canada (NSERC). R.F. acknowledges the financial support of the Banting postdoctoral fellowship of the NSERC and S.L. the financial support from Le Fonds de Recherche du Québec Nature et Technologies.

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Author notes

    • Enno Giese

    Present address: Institut für Quantenphysik and Center for Integrated Quantum Science and Technology, Universität Ulm, Ulm, Germany

    • Robert Fickler

    Present address: Photonics Laboratory, Physics Unit, Tampere University, Tampere, Finland


  1. Department of Physics, University of Ottawa, Ottawa, Ontario, Canada

    • Samuel Lemieux
    • , Enno Giese
    • , Robert Fickler
    •  & Robert W. Boyd
  2. Max Planck Institute for the Science of Light, Erlangen, Germany

    • Maria V. Chekhova
  3. Physics Department, Lomonosov Moscow State University, Moscow, Russia

    • Maria V. Chekhova
  4. University of Erlangen-Nuremberg, Erlangen, Germany

    • Maria V. Chekhova
  5. Institute of Optics, University of Rochester, Rochester, NY, USA

    • Robert W. Boyd


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M.V.C. conceived the idea for relative calibration. S.L., E.G. and R.F. extended that idea to the absolute calibration scheme. S.L. and R.F designed the experiment. S.L. conducted the experiment and performed the data analysis. S.L., E.G. and R.F. wrote the manuscript. M.V.C. and R.W.B. supervised the project. All authors contributed to scientific discussions.

Competing interests

S.L., M.V.C. and R.W.B., along with coinventors M. Manceau and G. Leuchs, the University of Ottawa and the Max Planck Institute for the Science of Light, have an international patent application (PCT/IB2017/056450) currently pending, about the relative calibration using PDC. E.G. and R.F. declare that they have no competing interests.

Corresponding author

Correspondence to Samuel Lemieux.

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