Ultrafast Coulomb blockade in an atomic-scale quantum dot

Controlling electron dynamics at optical clock rates is a fundamental challenge in lightwave-driven nanoelectronics and quantum technology. Here, we demonstrate ultrafast charge-state manipulation of individual selenium vacancies in monolayer and bilayer tungsten diselenide using picosecond terahertz source pulses, focused onto the junction of a scanning tunneling microscope. Using pump–probe time-domain sampling of the defect charge population, we capture atomic-scale snapshots of the transient Coulomb blockade, a hallmark of charge transport via quantized defect states. We leverage the Franck–Condon blockade, which restricts accessible vibronic transitions and promotes unidirectional charge transport, to effectively mitigate back tunneling to the tip electrode. Our master equation approach models the non-reciprocal tunneling process due to vibrations and angular momentum multiplicities, accurately reproducing the time-dependent tunneling current across different coupling regimes. Capturing and controlling ultrafast charge dynamics in low-dimensional materials at the atomic scale opens frontiers in lightwave-driven nanoscale science and technology.