Strong coupling and interfering resonances in isolated van der Waals nanoresonators

TL;DR

This paper reports the first observation of quasi-bound states in the continuum in isolated WS2 nanodisks, achieving exceptionally strong light-matter coupling with potential applications in photonics and quantum optics.

Contribution

It demonstrates polaritonic qBICs in van der Waals nanodisks driven by intrinsic Mie-resonance and exciton coupling, with polarization control enabling selective excitation.

Findings

Achieved Rabi splitting >310 meV, the largest in TMDC systems.

Validated existence of polaritonic qBICs via experimental measurements.

Showed polarization-dependent control of hybrid states.

Abstract

The study of strong light-matter interaction in van der Waals materials is at the forefront of current research in physics and chemistry, and it can be enhanced dramatically by employing resonances. Here we present the first observation of quasi-bound states in the continuum (qBICs) realized via polaritonic interfering resonances in isolated WS$_2$ nanodisks. We experimentally validate the existence of polaritonic qBICs driven by intrinsic coupling of Mie resonances and excitons. The system exhibits exceptionally strong light-matter interaction with a measured Rabi splitting exceeding 310 meV - the largest reported value among all transition metal dichalcogenide (TMDC) self-hybridized systems to date. The giant coupling strength stems from qBIC-induced in-plane field enhancement, which strongly interacts with in-plane excitonic dipoles while suppressing radiative losses. Polarization-controlled measurements further demonstrate selective excitation of qBIC through switching incident polarization to specific orthogonal configurations. The observed polarization-dependent coupling provides an additional degree of freedom to control over the hybrid states' spectral characteristics and spatial field distributions. Our demonstrations provide a pathway for engineering high-quality light-matter hybrid states in compact nanostructures, with potential applications in on-chip photonics, polaritonics, and quantum optics.