Sub-cycle control of optical properties by THz-induced dressed states

The laser dressing eigenstates of electronic systems in atoms leads to important quantum optical phenomena, such as Rabi splitting, optical Stark effect, and electromagnetically induced transparency, for the applications of ultrafast optical switching, slowed and stored light, and quantum information processing. In principle, a similar situation should be encountered in solids for hydrogen-like quasi-particles of excitons (electron-hole pairs). The intraexcitonic transition energy lies in the terahertz (THz) frequency range with large dipole moments, which making them fascinating system for exploiting THz excitonic interactions in optical communication devices. Here, we probe the transient absorption changes of near-infrared (NIR) pulse in a GaAs quantum well under the presence of a multi-cycle THz wave. By changing the delay between the NIR probe and the THz wave the absorption strengths are modulated on the sub-cycle THz timescale, and the frequency analysis shows the formation of THz-induced dressed states of excitons. Besides the novel concept for sub-cycle control of optical properties, our findings reveal the importance of accounting for interference effects of THz-induced nonlinear susceptibilities in the interpretation of THz pump–optical probe experiments.