Long-distance entanglement and quantum teleportation in XX spin chains

Isotropic XX models of one-dimensional spin-1/2 chains are investigated with the aim to elucidate the formal structure and the physical properties that allow these systems to act as channels for long-distance, high-fidelity quantum teleportation. We introduce two types of models: i open, dimerized XX chains, and ii open XX chains with small end bonds. For both models we obtain the exact expressions for the end-to-end correlations and the scaling of the energy gap with the length of the chain. We determine the end-to-end concurrence and show that model i supports true long-distance entanglement at zero temperature, while model ii supports “quasi-long-distance” entanglement that slowly falls off with the size of the chain. Due to the different scalings of the gaps, respectively exponential for model i and algebraic in model ii, we demonstrate that the latter allows for efficient qubit teleportation with high fidelity in sufficiently long chains even at moderately low temperatures.