Terahertz coherent control of the internal quantum state of dark excitons in Cu2O

Intense multi-terahertz fields of order MV/cm coherently promote 70% of the quasiparticles of an optically dark, dense, and cold 1s-para exciton gas in Cu
₂
O into the 2p state via a partial internal Rabi oscillation. Electro-optic sampling monitors the Larmor precession of the Bloch vector in real time.