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Quasi-phase-matched spontaneous parametric down-conversion in chiral ferroelectric nematic liquid crystals

Aljaž Kavčič1,2, Nerea Sebastián1, and Matjaž Humar1,2,3,*

  • *Contact author: matjaz.humar@ijs.si
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Phys. Rev. Research 8, 013119 – Published 2 February, 2026

DOI: https://doi.org/10.1103/wgb3-clj5

Abstract

For high-intensity photon pair generation via spontaneous parametric down-conversion, phase matching or quasi-phase-matching must be realized. The most common method is to use periodically poled crystals, where quasi-phase-matching is achieved through the periodic modulation of the nonlinear susceptibility. In contrast to solid-state materials typically employed, an alternative approach is demonstrated here by using chiral ferroelectric nematic liquid crystals (FNLCs). It involves the spontaneous formation of a twisted periodic arrangement of liquid crystal molecules that depends only on the concentration of chiral dopants. This enables the rapid and scalable fabrication of nonlinear optical media with a tunable periodicity of the structure. We show that within only 20µm, we can enhance the signal by 2 orders of magnitude compared to the maximal achievable rate for the non-phase-matched case. This process enables us to achieve a significantly enhanced photon pair generation rate of over 1200 Hz/mW in a very short interaction length while simultaneously maintaining a high degree of polarization entanglement. These results establish chiral FNLCs as a versatile, reconfigurable, and low-cost platform for nonlinear and quantum photonics.

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Phys. Rev. Research 8, 013119– Published 2 February, 2026
  • Received 21 July 2025
  • Revised 6 November 2025
  • Accepted 16 December 2025
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