We consider systems of two and three qubits, mutually coupled by
Heisenberg-type exchange interaction and interacting with external laser
fields. We show that these systems allow one to create maximally entangled Bell
states, as well as three qubit Greenberger-Horne-Zeilinger and W states. In
particular, we point out that some of the target states are the eigenstates of
the initial bare system. Due to this, one can create entangled states by means
of pulse area and adiabatic techniques, when starting from a separable
(non-entangled) ground state. On the other hand, for target states, not present
initially in the eigensystem of the model, we apply the robust stimulated Raman
adiabatic passage and π pulse techniques, that create desired coherent
superpositions of non-entangled eigenstates.Comment: 9 pages, 7 figures. Updated version for publicatio
