  We consider the perfect transfer of a state between arbitrary nodes of
one-dimensional spin-1/2 chain with optimally engineered couplings. Motivated
by the fact that such a system could be used as a data bus for connecting
multiple quantum processors, we derive two necessary and sufficient conditions
that have to be met in order to perfectly transfer a state between any two
nodes and we employ them to examine both open and closed geometries. Analytical
calculations and numerical optimizations are performed for both cases in order
to determine the reachability of certain target states and to provide optimal
values for the couplings which ensure perfect fidelity. An important finding is
that even-sized closed chains allow for perfect transfer between any pair of
sites and therefore are a promising platform for the implementation of data bus
protocols.

Quantum Physics