  We have investigated the analytical and numerical dynamics of entanglement
for two qubits that interact with each other via Heisenberg XXX-type
interaction and subject to local time-specific external kick and Gaussian
pulse-type magnetic fields in x-y plane. The qubits have been assumed to be
initially prepared in different pure separable and maximally entangled states
and the effect of the strength and the direction of external fast pulses on
concurrence has been investigated. The carefully designed kick or pulse
sequences are found to enable one to obtain constant long-lasting entanglement
with desired magnitude. Moreover, the time ordering effects are found to be
important in the creation and manipulation of entanglement by external fields.

Quantum Physics