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.