  Using a first-principles-based effective Hamiltonians within molecular
dynamics simulations, we discover that applying an electric field that is
opposite to the initial direction of the polarization results in a switching of
both the polarization and the magnetic chirality vector of multiferroic BiFeO3
at an ultrafast pace (namely of the order of picoseconds). We discuss the
origin of such a double ultrafast switching, which is found to involve original
intermediate magnetic states and may hold promise for designing various
devices.
