Engineering spin-spin interactions. (a), (b) Level scheme and setup for a possible implementation of spin-spin interactions in 171Yb+. (c), (d) Interaction strengths between one ion in the center and the other ions, for (c) or (d) , and different detunings from the center-of-mass (COM) mode. We have used the parameters specified in (b). Interactions are compared with the interactions of the Haldane-Shastry (HS) model (brown lines), and with interactions (green lines).