[论文解读] Enhanced nonlinear interaction of polaritons via excitonic Rydberg states in monolayer WSe2

Jie Gu, Valentin Walther+8 more|arXiv (Cornell University)|Dec 28, 2019

Strong Light-Matter Interactions参考文献 38被引用 15

一句话总结

该论文通过在单层WSe2中利用第一激发激子态（类里德伯格态），实现了激子极化激元中增强的非线性相互作用。由于这些激发激子具有更大的空间扩展范围，极化激元的非线性响应提高了十倍以上，这一结果通过可测量的腔体拉比劈裂变化得到证实，标志着在固态系统中实现强单光子非线性效应的重要进展。

ABSTRACT

Strong optical nonlinearities play a central role in realizing quantum photonic technologies. In solid state systems, exciton-polaritons, which result from the hybridization of material excitations and cavity photons, are an attractive candidate to realize such nonlinearities. Here, the interaction between excitons forms the basis of the polaritonic nonlinearity. While the interaction between ground state excitons generates a notable optical nonlinearity, the strength of such ground state interactions is generally not sufficient to reach the regime of quantum nonlinear optics and strong single-polariton interactions. Excited states, however, feature enhanced interactions and therefore hold promise for accessing the quantum domain of single-photon nonlinearities, as demonstrated with high-lying Rydberg states of cold atomic systems. Excitons in excited states have recently been observed in monolayer transition metal dichalcogenides. Here we demonstrate the formation of exciton-polaritons using the first excited excitonic state in monolayer tungsten diselenide (WSe2) embedded in a microcavity. Owing to the larger exciton size compared to their ground state counterpart, the realized polaritons exhibit an enhanced nonlinear response by more than an order of magnitude, as evidenced through a modification of the cavity Rabi splitting. The demonstration of excited exciton-polaritons in two-dimensional semiconductors and their enhanced nonlinear response presents the first step towards the generation of strong photon interactions in solid state systems, a necessary building block for quantum photonic technologies.

研究动机与目标

• 探索二维半导体中增强的光学非线性效应，以实现量子光子学应用。
• 研究单层WSe2中的激发态激子是否能产生强于基态激子的极化激元非线性效应。
• 证明利用类里德伯格激子态在固态系统中实现强单极化激元相互作用的可行性。
• 通过腔体拉比劈裂的可测量位移，量化非线性响应的增强程度。

提出的方法

• 通过将单层WSe2中的第一激发激子态与微腔模耦合，形成激子极化激元。
• 通过光学激发填充具有显著大于基态空间扩展范围的类里德伯格激子态。
• 通过在增加抽运功率下测量腔体拉比劈裂的变化，探测非线性响应。
• 增强的相互作用强度源于类里德伯格态中空间扩展激子之间的偶极-偶极相互作用增强。
• 在低温下进行测量，以保持相干性并增强多体效应。
• 理论建模支持这一解释：观察到的非线性增强源于激发态中激子尺寸的增大。

实验结果

研究问题

• RQ1 在单层WSe2中使用激发激子态是否能导致极化激元非线性效应的可测量增强？
• RQ2 WSe2中类里德伯格激子的空间扩展范围如何影响微腔中光子-光子相互作用的强度？
• RQ3 与基态相比，通过占据更高能级的激子态，激子极化激元的非线性响应能增强到何种程度？
• RQ4 观察到的非线性增强是否与基于偶极-偶极相互作用增强的理论预期一致？

主要发现

• 由单层WSe2中第一激发激子态形成的极化激元，其非线性响应相比基态极化激元增强了一个数量级以上。
• 该增强效应通过在增加抽运强度下腔体拉比劈裂的显著变化得到直接证实。
• 观察到的非线性增强归因于类里德伯格激子更大的空间扩展范围，从而增强了其偶极-偶极相互作用强度。
• 本工作首次实现了在二维半导体中具有可测量且显著非线性响应的激发激子极化激元。
• 该结果为在固态平台中实现强单光子非线性效应以推动量子光子技术的发展迈出了关键一步。