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  • Open Access

Certifying Non-Classicality and Non-Gaussianity Through Optical Parametric Amplification

Mahmoud Kalash1,2,*, M. H. M. Passos1,4, Éva Rácz3, László Ruppert3, Radim Filip3, and Maria V. Chekhova1,2,†

  • *Contact author: mahmoud.kalash@mpl.mpg.de
  • †Contact author: maria.chekhova@mpl.mpg.de
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PRX Quantum 7, 033020 – Published 30 July, 2026

DOI: https://doi.org/10.1103/j68x-skmn

Abstract

Non-Gaussian states of light are essential for numerous quantum information protocols; thus, certifying non-Gaussianity (NG) is crucial. Full quantum state tomography, commonly used for this purpose, is complicated and yields inconclusive results for strongly mixed states. Certifying NG through directly measurable parameters is a simpler alternative, typically achieved by measuring photon-number probabilities—either directly, using photon-number resolving detectors, or through Hanbury Brown-Twiss type measurements with single-photon detectors. Here, we demonstrate, theoretically and experimentally, that phase-sensitive optical parametric amplification (OPA), followed by conventional intensity detection, can effectively replace this approach. Our proposed witness relies on the mean photon number (relative to that produced by the amplifier without any input) and the second-order correlation function after OPA. Both can be directly obtained from the measured amplified intensity and are invariant to detection losses. The method therefore requires neither photon-number resolution nor high detection efficiency. In a proof-of-principle experiment, we successfully certify the quantum NG of a heralded quasi-single-photon state. Since OPA is a broadband and multimode process, our method provides a foundation for developing high-dimensional quantum technologies utilizing broadband multimode non-Gaussian states.

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Popular Summary

Non-Gaussian states of light are among the strangest forms of quantum light, but they are also essential for many quantum technologies. Some key tasks, such as quantum error correction, cannot be achieved without them. Detecting whether a light state is non-Gaussian is therefore an important challenge. Traditionally, this requires sophisticated and costly single-photon detectors or even detectors capable of resolving the number of photons. In this work, we show that an optical parametric amplifier can strengthen the signature of non-Gaussianity, making it detectable with simple intensity detectors such as cameras. This approach greatly simplifies the experimental verification of quantum non-Gaussianity. We demonstrate the method by characterizing single-photon states mixed with vacuum, as well as two-photon states, highlighting a practical route toward more accessible quantum photonic technologies.

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PRX Quantum 7, 033020– Published 30 July, 2026
  • Received 20 October 2025
  • Accepted 3 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by Max Planck Society.

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