Joachim Stolze, Gonzalo A. Álvarez, Omar Osenda, and Analia Zwick
To appear in Georgios M. Nikolopoulos and Igor Jex, editors:
Quantum State Transfer and Quantum Network Engineering. Springer Series in Quantum Science and Technology, Springer, Berlin 2013.
Spin chains are linear arrangements of qubits (spin-1/2 objects) with interactions between nearest or more distant neighbors. They have been considered for quantum information transfer between subunits of a quantum information processing device at short or intermediate distances. The most frequently studied task is the transfer of a single-qubit state. Several protocols have been developed to achieve this goal, broadly divisible into two classes, fully-engineered and boundary- controlled spin chains. We discuss state transfer induced by the natural dynamics of these two classes of systems, and the influence of deviations from the ideal system configuration, that is, manufacturing errors in the nearest-neighbor spin couplings. The fidelity of state transfer depends on the chain length and the disorder strength. We observe a power-law scaling of the fidelity deficit, i.e. the deviation from perfect transfer. Boundary-controlled chains can provide excellent fidelity under suitable circumstances and are potentially less difficult to manufacture and control than fully-engineered chains. We also review other existing theoretical work on the robustness of quantum state transfer as well as proposals for experimental implementation.