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Toward spectral engineering of squeezed light in high-gain parametric down-conversion

Jatin Kumar1,*, Aleksa Krstić1, Sina Saravi1,2,3,4, and Frank Setzpfandt1,5

  • *Contact author: jatin.kumar@uni-jena.de
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Phys. Rev. A 114, 023706 – Published 10 August, 2026

DOI: https://doi.org/10.1103/2hth-yy33

Abstract

We investigated the spectral properties of squeezed light generated via parametric down-conversion in the high-gain regime, considering both unapodized and apodized dispersion-engineered waveguides. The gain-dependent evolution of these states is examined starting from the low-gain regime, which includes both highly correlated and nearly uncorrelated cases. For the unapodized configuration, our simulated results show a monotonic increase in spectral purity with gain, whereas for some of the apodized configuration, they exhibit a nonmonotonic dependence, initially decreasing and then recovering at higher gain. By combining Schmidt-mode analysis with a group-velocity-based interpretation, we explain why different dispersion conditions exhibit distinct gain-dependent behavior, specifically that rapid purification occurs when the pump group velocity lies between those of the signal and idler. Our study shows that the evolution of spectral purity is governed primarily by the underlying dispersion of the waveguide. These results demonstrate that dispersion engineering and parametric gain can be jointly exploited to tailor the spectral-mode structure of squeezed-light sources, enabling their optimization for a broad range of quantum applications.

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Phys. Rev. A 114, 023706– Published 10 August, 2026
  • Received 15 January 2026
  • Revised 25 June 2026
  • Accepted 17 July 2026
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