In the future, ultrahigh-speed spintronics will require ultrafast coherent magnetization reversal within a picosecond—one-trillionth of a second. Spintronics centers on an electron’s spin and magnetic moment in solid-state devices. While this may eventually be achieved via irradiation with a nearly monocyclic terahertz pulse, the small change of magnetization, or modulation, it generates has so far prevented any practical application of this technique.