近日，德国埃尔朗根-纽伦堡大学的Maria V. Chekhova及其研究团队取得一项新进展。经过不懈努力，他们成功在液晶中产生可调谐纠缠光子对。相关研究成果已于2024年6月12日在国际权威学术期刊《自然》上发表。

该研究团队在铁电向列液晶中实现了自发参数下转换，并展示了电场可调谐的纠缠光子宽带产生过程，其效率可与最佳非线性晶体相媲美。施加几伏电压或沿样品方向扭曲分子取向，光子对的发射速率和偏振态会发生显著变化。液晶源可以实现一种特殊类型的准相位匹配，这种匹配基于分子扭曲结构，因此可以根据光子对的所需光谱和偏振特性进行重新配置。这种光源有望在功能、亮度和所产生量子态的可调性方面优于标准非线性光学材料。这里发展的概念可以扩展到复杂的拓扑结构，宏观器件和多像素可调量子光源。

据悉，液晶凭借其自组装能力、对电场的强响应能力以及易于集成到复杂系统中的特性，已成为光束操纵的关键材料。最新研究发现，铁电向列液晶还展现出显著的二阶光学非线性，因此被视为非线性光学的潜在材料。作为量子光源，它们有望极大地拓宽光子量子技术的应用领域。然而，尽管自发参数下转换是产生纠缠光子的基本途径，且预示着单光子和压缩光的产生，但这一现象至今尚未在液晶或任何液体、有机材料中观察到。

附：英文原文

Title: Tunable entangled photon-pair generation in a liquid crystal

Author: Sultanov, Vitaliy, Kavcic, Aljaz, Kokkinakis, Emmanouil, Sebastin, Nerea, Chekhova, Maria V., Humar, Matjaz

Issue&Volume: 2024-06-12

Abstract: Liquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation. The recently discovered ferroelectric nematic liquid crystals also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics. Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies. However, spontaneous parametric down-conversion, the basic source of entangled photons, heralded single photons and squeezed light, has so far not been observed in liquid crystals—or in any liquids or organic materials. Here we implement spontaneous parametric down-conversion in a ferroelectric nematic liquid crystal and demonstrate electric-field tunable broadband generation of entangled photons, with an efficiency comparable to that of the best nonlinear crystals. The emission rate and polarization state of photon pairs is markedly varied by applying a few volts or twisting the molecular orientation along the sample. A liquid-crystal source enables a special type of quasi-phase matching, which is based on the molecular twist structure and is therefore reconfigurable for the desired spectral and polarization properties of photon pairs. Such sources promise to outperform standard nonlinear optical materials in terms of functionality, brightness and the tunability of the generated quantum state. The concepts developed here can be extended to complex topological structures, macroscopic devices and multi-pixel tunable quantum light sources.

DOI: 10.1038/s41586-024-07543-5

Source: https://www.nature.com/articles/s41586-024-07543-5