  A communication protocol is proposed in which quantum state transfer is
mediated by a vibrational exciton. We consider two distant molecular groups
grafted on the sides of a lattice. These groups behave as two quantum computers
where the information in encoded and received. The lattice plays the role of a
communication channel along which the exciton propagates and interacts with a
phonon bath. Special attention is paid for describing the system involving an
exciton dressed by a single phonon mode. The Hamiltonian is thus solved exactly
so that the relevance of the perturbation theory is checked. Within the
nonadiabatic weak-coupling limit, it is shown that the system supports three
quasi-degenerate states that define the relevant paths followed by the exciton
to tunnel between the computers. When the model parameters are judiciously
chosen, constructive interferences take place between these paths.
Phonon-induced decoherence is minimized and a high-fidelity quantum state
transfer occurs over a broad temperature range.
