Consider a system in the initial state , which we aim to efficiently transfer to the final state using an intermediate resonant state, see Fig. 1b and Supplementary Note 2. The initial and final states have the same energy of , where h ≡ h2,3 (as is the standard convention in quantum optics, we refer to the expectation value of the Hamiltonian in a given state as the energy of this state). In turn, the eigenstates of Hamiltonian (1) in the single excitation space of strongly coupled sites j=2,3 are given by , with the corresponding energies split by 2J2. Then, by a proper choice of the magnetic field, , we can tune the energy of one of the intermediate states into resonance with the initial and final states (for example, for h=h− the resonant state is ). Simultaneously, the other intermediate state does not participate in the transfer since its energy is detuned by 2J2 which is much larger than the exchange coupling of the initial and final states to the intermediate states. The transfer time of the spin excitation between the initial and final states via a single resonant intermediate state is tout=π/|J1| (Fig. 1d).