Ultrastrong coupling (USC) between phonons and vacuum photons can result in fascinating quantum phenomena, though it is difficult to achieve due to the small dipole moments of phonons in solids. Here, we investigate the vacuum Rabi splitting by coupling phonons in perovskite $\mathrm{C}{\mathrm{H}}_3\mathrm{N}{\mathrm{H}}_3\mathrm{Pb}{\mathrm{I}}_3$ films with photons in split ring resonators. As the gap size of the resonator decreases, the coupling strength η increases due to the enhanced vacuum field in the gap, reaching the USC regime $(\eta \sim 0.24)$ at a gap size of 100 nm. Our results show that nanoresonators are an excellent platform for studies of vacuum-dressed phonon properties.

中文翻译：

---

增强真空电场引起的太赫兹声子和光子之间的超强耦合

声子和真空光子之间的超强耦合 (USC) 可以产生迷人的量子现象，但由于固体中声子的偶极矩很小，因此很难实现。在这里，我们通过在钙钛矿中耦合声子来研究真空 Rabi 分裂$\mathrm{C}{\mathrm{H}}_3\mathrm{N}{\mathrm{H}}_3铅{\mathrm{一世}}_3$在裂环谐振器中具有光子的薄膜。随着谐振器的间隙尺寸减小，由于间隙中增强的真空场，耦合强度η增加，达到 USC 状态$(\eta ～0.24)$间隙尺寸为 100 nm。我们的结果表明，纳米谐振器是研究真空修饰声子特性的绝佳平台。