Spin network communication protocols

Quantum network can be used as communication lines to connect regions of high control. In this setting we analyze several protocols that allow one to achieve perfect quantum state transfer. We also demonstrate a scheme for controlling a large quantum system by acting on a small subsystem only. The local control is mediated to the larger system by some fixed coupling Hamiltonian. The scheme allows transferring arbitrary and unknown quantum states from a memory on the large system (“uploadaccess”) as well as the inverse (“downloadaccess”). We study sufficient conditions of the coupling Hamiltonian and give lower bounds on the fidelities for downloading and uploading.