Driving electrons by atomically strong optical fields, non-perturbative dynamics such as the generation of high harmonic or high-order sideband radiation can arise, allowing for a detailed insight into the carrier dynamics, switching spins and building quasiparticle accelerators. In a complementary limit, electrons can be dressed solely by vacuum field fluctuations in microcavities, which results in the formation of new light-matter hybridized eigenstates – the foundation of cavity quantum electrodynamics.
In our group we push the limit of light-matter interaction to the ultrastrong and deepstrong coupling regime, where light and matter exchange energy faster than their fundamental oscillation period. Here anti-resonant interactions govern the dynamics, giving rise to a modified vacuum ground state and novel quantum effects. By reaching coupling strengths of unprecedented levels, we even get a nonzero population of vacuum photons in the ground state. In our group we have pioneered ultrafast control and custom-tailoring of this exciting regime, exploring nonlinear dynamics and more quantum phenomena of ultra- and deepstrong light-matter coupling.