Figure 1

In the first scenario (\(J\ne 0,D=0\)) the concurrence as a function of time t (a) \(J=-0.25\), (b) \(J=-0.5\), (c) \(J=0.75\). As can be seen, the maximum value of the concurrence function for the various pairs occurs in the shorter time instances as J increases, and the graphs become more compact as a result. The diagram of \(X-t_{Max}\) for different values of exchange interaction is presented in panel (d), from which the value of propagation speed for \(J=-0.5\) is \(0.4410\pm 0.0005\), for \(J=0.75\) and \(J=-1.0\), this quantity equals with \(0.6620 \pm 0.0005\) and \(0.8830 \pm 0.0005\) respectively and for all plots \(\phi =0\).