  Heisenberg spin chains can act as quantum wires transferring quantum states
either perfectly or with high fidelity. Gaussian packets of excitations passing
through dual rails can encode the two states of a logical qubit, depending on
which rail is empty and which rail is carrying the packet. With extra
interactions in one or between different chains, one can introduce interaction
zones in arrays of such chains, where specific one or two qubit gates act on
any qubit which passes through these interaction zones. Therefore universal
quantum computation is made possible in a static way where no external control
is needed. This scheme will then pave the way for a scalable way of quantum
computation where specific hardwares can be connected to make large quantum
circuits. Our scheme is an improvement of a recent scheme where we have
achieved to borrow an idea from quantum electrodynamics to replace non-local
interactions between spin chains with local interactions mediated by an
ancillary chain.
