  Information can be stored magnetically in antiferromagnets ultrafast since
their characteristic times are on the picosecond scale. Various spin torques
have proven to be important for efficient and high-speed magnetic memories. So
far, this has been understood on the classical level by solving the equations
of motion for macrospins describing the collective motion of the sublattice
magnetizations. Since spins and hence magnetizations are deeply rooted in
quantum mechanics, we show that the exchange enhanced manipulation of
sublattice magnetizations extends to quantum antiferromagnets as well. To this
end, we solve the time-dependent mean-field equations for Schwinger boson
theory under external alternating magnetic fields. Exchange enhancement
persists on the quantum level which includes dephasing effects. Significantly
lower fields are sufficient to control the sublattice magnetization than for
uniform fields which holds great promises for the realization of ultrafast
magnetic storage devices.
