Spin chains have been proposed as quantum wires in many quantum information
processing architectures. Coherent transmission of quantum information over
short distances is enabled by their internal dynamics, which drives the
transport of single-spin excitations in perfectly polarized chains. Given the
practical challenge of preparing the chain in a pure state, we propose to use a
chain that is initially in the maximally mixed state. We compare the transport
properties of pure and mixed-state chains, finding similarities that enable the
experimental study of pure-state transfer by its simulation via mixed-state
chains, and demonstrate protocols for the perfect transfer of quantum
information in these chains. Remarkably, mixed-state chains allow the use of
Hamiltonians which do not preserve the total number of excitations, and which
are more readily obtainable from the naturally occurring magnetic dipolar
interaction. We propose experimental implementations using solid-state nuclear
magnetic resonance and defect centers in diamond.Comment: 9 page
