  We consider a spin-1/2 anisotropic XY model with time-dependent spin-spin
coupling as means of creating long-distance entanglement. We predict the
emergence of significant entanglement between the first and the last spin
whenever the ac part of the coupling has a frequency matching the Zeeman
splitting. In particular, we find that the concurrence assumes its maximum with
a vanishing dc part. Mapping the time-dependent Hamiltonian within a
rotating-wave approximation to an effective static model provides qualitative
and quantitative understanding of this entanglement resonance. Numerical
results for the duration of the entanglement creation and its length dependence
substantiate the effective static picture.
