Information Transfer and Entanglement Creation by Spin Chains: Effects of Noise and Asymmetry

For the transfer of quantum information and the creation of entangled states, the application of tuned spin chains, systems of spins with the nearest-neighbor coupling tuned so as to give high efficiency, has been proposed and some examples of high performance have been given by several authors. In this article, the effect of deviations from tuned values and the effect of resultant asymmetry are investigated through numerical simulations and theoretical analyses. It is shown that there exists a system where the transfer efficiency is comparable with exactly tuned ones and, at the same time, robust to noises in the coupling constants. It is also shown that the effect of asymmetry on the efficiency of entanglement creation is of the second order when the asymmetry is small.