Fig. 4. Schemes for spin network applications.

(A) Schematic representation of the envisaged probe–controlled spin network (with intracell and intercell couplings, J and J′, respectively), equipped with an atomic force microscopy magnetic tip to generate gradient fields on nanometer length scales. (B) Extension of the multi-electron spectroscopy to extract intercell couplings, which can further lead to the structural analysis of the spin network. By varying the π pulse time on the second τ, we arrive at the Fourier components of the observed probe spin response. (C) Remote communication between two probes via a spin chain is shown, where the response on the probe spin B, ${\mathit{P}}_{\mathit{B}}(\mathit{t})=<{\mathit{S}}_{\mathit{B}}^{\mathit{z}}>$, varies by sweeping the frequency of the probe A. When ω_A = ω_B, the quantum state of probe A is transferred to B. (D) The effect of the quantum critical point (QCP) in a transverse Ising chain on the state transfer between the two remote probes. At QCP corresponding to ω = J, the fidelity drastically increases—indicating enhanced long-range correlations in the chain.