Frontiers of sub-cycle terahertz science: The fast, the strong and the small

Phase-locked few-cycle pulses in the ultrabroadband terahertz (THz) spectral window
^1-4
have become a powerful tool to access low-energy elementary dynamics in solids, on time scales shorter than a single oscillation cycle of light
^5-14
. Here, we tackle the role of excitons and their dynamics in modern dichalcogenide monolayers and exciton-polariton condensates
^7-9
. Furthermore, intense THz pulses are used as atomically strong bias fields to explore high-harmonic generation by dynamical Bloch oscillations in bulk solids
^11-13
. Finally, we develop a novel microscope that introduces sub-cycle resolution on the few-nm length scale
¹⁴
. The experiments reviewed here challenge modern quantum theories and spark hope for electronics and magnetic storage at optical clock rates.