Entangled photons are a key resource in quantum technologies. While intense laser light propagating in nonlinear crystals is conventionally used to generate entangled photons, such schemes have low efficiency due to the weak nonlinear response of known materials and losses associated with in/out photon coupling. Here, we show how to generate entangled polariton pairs directly within optical waveguides using free electrons. The measured energy loss of undeflected electrons heralds the production of counter-propagating polariton pairs entangled in energy and emission direction. For illustration, we study the excitation of plasmon polaritons in metal strip waveguides that strongly enhance light-matter interactions, rendering two-plasmon generation dominant over single-plasmon excitation. We demonstrate that electron energy losses detected within optimal frequency ranges can reliably signal the generation of plasmon pairs entangled in energy and momentum. Our proposed scheme is directly applicable to other types of optical waveguides for in situ generation of entangled photon pairs.

中文翻译：

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由自由电子产生纠缠波导光子对

纠缠光子是量子技术的关键资源。虽然在非线性晶体中传播的强激光通常用于产生纠缠光子，但由于已知材料的弱非线性响应以及与输入/输出光子耦合相关的损耗，这种方案效率较低。在这里，我们展示了如何使用自由电子直接在光波导内生成纠缠极化子对。测量到的未偏转电子的能量损失预示着在能量和发射方向上纠缠的反向传播极化子对的产生。为了说明这一点，我们研究了金属带波导中等离子体激元的激发，其强烈增强了光与物质的相互作用，使得双等离子体激元的产生比单等离子体激元的激发占主导地位。我们证明，在最佳频率范围内检测到的电子能量损失可以可靠地发出与能量和动量纠缠的等离子体对的生成信号。我们提出的方案可直接适用于其他类型的光波导，用于原位生成纠缠光子对。