Valley-selective optical Stark effect of exciton-polaritons in monolayer WS₂

Light provides a high-speed coherent medium for measurement and manipulation of electronic quantum states. Exploiting the optical selection rules of transition metal dicalchogenide monolayers (TMDs), the optical Stark effect allows for valley-selective control of energy levels using sub-resonant optical pulses. Recent discoveries have shown that microcavity exciton-polaritons in TMDs preserve valley features while also incorporating properties of light that can enhance valley properties. Here, we demonstrate valley-selective control of polariton energies in WS₂ using the optical Stark effect. Transient reflectance measurements reveal polariton spectra with strong polarization contrast originating from valley-selective energy shifts. The shifts are well-understood using a transfer matrix model of the coupled exciton-cavity structure. This robust, valley-selective control over TMD polaritons establishes a powerful new approach for coherent manipulation of hybrid light-matter states with valley sensitivity.