Encoding and manipulating ultrafast coherent valleytronic information with lightwaves

We employ sequences of phase-locked, few-cycle visible laser pulses to coherently control the valley pseudospin in monolayer WS 2 ​ . By adjusting the relative timing of the optical field oscillations with sub-femtosecond accuracy, we demonstrate that two temporally delayed pulses with orthogonal linear polarizations generate a valley-selective carrier population. Introducing an additional pulse pair enables ultrafast logical operations, including suppression and restoration of the valley excitation, at room temperature and with switching frequencies reaching 10 THz. This approach further allows us to separately probe the decay of valley polarization and the excitonic coherence time, providing a pathway toward low-energy ultrafast information technologies driven by readily available few-cycle optical pulses.