Ultrafast valleytronic logic operations

Today’s information processing technology relies on electronics, with transistor switches reaching speeds as high as 800 GHz yet appearing to approach their intrinsic limits set by charge carrier transit times. The next disruptive step towards increasing the speed of information processing could come from driving the electronic response in solids with ultrafast controlled lightwaves. This lightwave electronics aims to use ultrashort pulses of light to switch electric currents and can potentially operate at nearly PHz rates. Lightwave valleytronics targets a new degree of freedom for information processing offered by two-dimensional materials: the valley pseudospin. Here we use a sequence of phase-locked few-optical-cycle visible pulses to excite and switch the valley pseudospin in a WS2 monolayer. By timing the carrier oscillations with sub-femtosecond precision, we show that a pair of pulses separated in time with linear orthogonal polarizations can induce a valley selective population. Adding a second pair of pulses, we perform logic operations such as valley de-excitation and re-excitation at room temperature at rates as high as ∼ 10 THz. Our experimental method also allows independent measurement of the valley polarization decay and the excitonic decoherence time. Our work opens a new route for ultrafast information processing with low-power few-optical-cycle light pulses available today.