  Pairwise quantum correlations in the ground state of a N-spins
antiferromagnetic chain described by the Heisenberg model with nearest neighbor
exchange coupling are investigated. By varying a single coupling between two
neighboring sites it is possible to drive spins from entangled to disentangled
states, reversibly. For even N the two-spin density matrix is written in the
form of a Werner state, allowing identification of the weight parameter with
the usual spin-spin correlation function $\langle S_i^z \, S_j^z \rangle =
\Gamma_{ij}$. The correlation functions show universal behavior in the
$\Gamma$-dependence. This study presents a concrete possibility for the
practical demonstration of entanglement control, opening alternatives for
probing non-classical correlations and the realization of Werner states in
familiar condensed matter systems. All required fabrication and measurement
ingredients are currently available.
