Fig. 2. Characterization of the Ising interaction and the effective potential of the topological defect.

(A) The heatmap of the theoretical spin-spin coupling coefficients J_ij in a 21-ion chain, which is calculated from independently calibrated experimental parameters. (B) Measured spin-flip energies (blue dots) versus the calculated values (red dots) using the J_ij matrix in (A). Error bars of the experimental data represent 1 SD. The error band of the theoretical results accounts for a laser frequency fluctuation of ±2π × 500 Hz. (C) The effective potential of the kink calculated from the J_ij matrix. We have redefined the zero point of the potential at the center.