Giant AC Stark effect in a strongly-coupled light-matter system

Summary form only given. Strong light-matter interaction in semiconductor microcavities manifested in new dressed eigenstates - exciton-polaritons, has been of great interest in the last decade, resulting in various exciting and intricate phenomena including high-temperature Bose-Einstein condensation and superfluid behaviour [1-3]. A novel approach to provide dynamic energy shifts for exciton-polaritons was recently demonstrated based on the AC Stark effect [4], enabling ultrafast switching [5], phase imprinting and modulating potential landscapes faster than the condensate coherence time. However, the magnitude of the fast AC-Stark-based modulation in standard microcavities is limited to the weak perturbative regime.Here we demonstrate for the first time, modulation of a strongly coupled light-matter system - stronger than the Rabi splitting and more than an order of magnitude stronger than previous observations. A specially designed high-quality microcavity with the bottom Bragg reflector spectrally-shifted relative to the top reflector, transmits the AC Stark pump pulse into the cavity but not into the substrate, thus eliminating substrate heating at high pump powers. We observed a non-resonant AC Stark shift which was greater than the Rabi splitting between upper and lower polaritons (Fig.1). In previous experiments, the energy shift of the polariton levels was treated perturbatively assuming a small energy shift of the exciton levels alone [4]. In our case this assumption is no longer valid, therefore full Hamiltonian diagonalization has been performed. The shift was measured as a function of pump intensity and a wide range of temperatures on a fs time scale. The measured dynamical behaviour is in good agreement with our full non-perturbative theoretical model.