On-chip photonic crystal dressed Rydberg exciton polaritons with enhanced nonlinearity in monolayer WS₂

Rydberg exciton polaritons are promising for quantum optoelectronic devices exploiting their strong optical nonlinearities. Conventional polaritonic devices consist of optical microcavities made by vertically stacking distributed Bragg reflectors (DBR) and/or metallic mirrors and excitonic active regions, which may restrain their applicability in photonic integrated technologies. Here, we demonstrate the first on-chip photonic crystal (PhC) Rydberg polaritons based on monolayer WS₂, which survive up to 80 K. These Rydberg polaritons exhibit a nonlinearity 8.0 ± 2.3 times larger than that of the ground polaritonic states due mostly to their extended exciton radii and, additionally, due to a stronger spatially localized electric field distribution compared to the dual-DBR geometry. Furthermore, the coexistence of 2s and 1s polaritonic states enables us to experimentally quantify their cross-interaction constant (14.4 ± 6.8 μeV μm²). The first realization of on-chip Rydberg polaritons represents a solid step towards polaritonic-based integrated circuits.