  We propose an all optical ultrafast method to highly magnetize general
quantum magnets using a circularly polarized terahertz laser. The key idea is
to utilize a circularly polarized laser and its chirping. Through this method,
one can obtain magnetization curves of a broad class of quantum magnets as a
function of time even without any static magnetic field. We numerically
demonstrate the laser-induced magnetization process in realistic quantum spin
models and find a condition for the realization. The onset of magnetization can
be described by a many-body version of Landau-Zener mechanism. In a particular
model, we show that a plateau state with topological properties can be realized
dynamically.
