Electrically and Geometrically Tunable Photon Pair Entanglement from Ferroelectric Nematic Liquid Crystal

Entangled photons represent one of the key building blocks of modern quantum technologies. In our study Electrically and Geometrically Tunable Photon Pair Entanglement from Ferroelectric Nematic Liquid Crystal, published in Advanced Science, we demonstrated that quantumly entangled photon pairs can be generated in ferroelectric nematic liquid crystals (FNLCs), while simultaneously enabling continuous tuning of their degree of entanglement.

We showed that the thickness of the liquid crystal sample, in combination with the molecular twist, has a significant impact on the quantum state of the photons generated via spontaneous parametric down-conversion. By appropriately varying these two parameters, it is possible to transition from separable to fully entangled states (within the limits of experimental uncertainty). Furthermore, we demonstrated that the degree of entanglement can be dynamically controlled in real time using an external electric field, which influences the molecular orientation within the sample.

The ability to achieve fast and straightforward electrical control over molecular orientation—and consequently over the quantum state—constitutes a key advantage of liquid crystals compared to conventional solid-state nonlinear crystals. These results point toward the development of so-called “quantum displays,” in which each pixel would function as an independent, electronically controlled quantum light source.

S. Klopčič, A. Kavčič, N. Sebastián, and M. Humar, “ Electrically and Geometrically Tunable Photon Pair Entanglement from Ferroelectric Nematic Liquid Crystal.” Adv. Sci. (2025): e15206. https://doi.org/10.1002/advs.202515206.