Ultrastrong coupling between THz phonons and photons caused by an enhanced vacuum electric field
Zhenya Zhang, Hideki Hirori, Fumiya Sekiguchi, Ai Shimazaki, Yasuko Iwasaki, Tomoya Nakamura, Atsushi Wakamiya, Yoshihiko Kanemitsu
Abstract
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 CH 3 NH 3 PbI 3 films with photons in split ring resonators. As the gap size of the resonator decreases, the coupling strength increases due to the enhanced vacuum field in the gap, reaching the USC regime ( 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.