Source: https://www.nature.com/articles/s41567-019-0447-2?error=cookies_not_supported&code=7f4e478c-97cf-4e1b-8860-da828ca99ec7
Timestamp: 2019-04-19 10:37:32+00:00

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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.
The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.
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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.
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.
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.

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