  We theoretically study THz-light-driven high-harmonic generation (HHG) in the
spin-liquid states of the Kitaev honeycomb model with a magnetostriction
coupling between spin and electric polarization. To compute the HHG spectra, we
numerically solve the Lindblad equation, taking account of the dissipation
effect. We find that isotropic Kitaev models possess a dynamical symmetry,
which is broken by a static electric field, analogous to HHG in electron
systems. We show that the HHG spectra exhibit characteristic continua of
Majorana fermion excitations, and their broad peaks can be controlled by
applying static electric or magnetic fields. In particular, the magnetic-field
dependence of the HHG spectra drastically differs from those of usual ordered
magnets. These results indicate that an intense THz laser provides a powerful
tool to observe dynamic features of quantum spin liquids.
