Strong light-matter coupling between excitons and chiral quasi-bound states in the continuum in van der Waals metasurfaces

The study of strong coupling between photonic cavities and excitons has brought about significant advances, varying from fundamental physics to applied science. However, there are several challenges hindering its further development, including obtaining photonic modes with both low room-temperature loss and high electric field (EF) enhancements, the difficulty of precisely transferring exciton materials into the photonic cavity, and the urgent need for additional manipulation approaches. In order to overcome these challenges simultaneously, we present a theoretical strong coupling system based on the chiral metasurfaces that are built by the excitonic van der Waals material of WSe2 and can support the quasi-bound states in the continuum (q-BIC) mode. The q-BIC mode can sustain EF enhancements over 80 times with loss smaller than 10 meV, and the strong coupling between q-BIC mode and WSe2 excitons can be naturally realized without material transferring. Furthermore, a large chirality beyond 0.98 can be obtained in this strong coupling system, making the circular polarization of excitation light an effective parameter to control the generation of coherent states in this metasurface system. Our results can benefit the further development of strong coupling research, shedding light onto the exploration of new quantum devices.