  We investigate the ability of dimerized spin chains with defects to generate
EPR pairs to very high fidelity through their natural dynamics. We propose two
protocols based on different initializations of the system, which yield the
same maximally entangled Bell state after a characteristic time. This
entangling time can be varied through engineering the weak/strong couplings'
ratio of the chain, with larger values giving rise to an exponentially faster
quantum entangling operation. We demonstrate that there is a set of
characteristic values of the coupling, for which the entanglement generated
remains extremely high. We investigate the robustness of both protocols to
diagonal and off-diagonal disorder. Our results demonstrate extremely strong
robustness to both perturbation types, up to strength of 50% of the weak
coupling. Robustness to disorder can be further enhanced by increasing the
coupling ratio. The combination of these properties makes the use of our
proposed device suitable for the rapid and robust generation of Bell states in
quantum information processing applications.
