Figure 3. Finding the ground state of He–H⁺ for a specific molecular separation R=90 pm.

(a) Experimentally computed energy ‹› (coloured dots) as a function of the optimization step j. The colour represents the tangle (degree of entanglement) of the physical state, estimated directly from the state parameters . The red lines indicate the energy levels of (R). The optimization algorithm clearly converges to the ground state of the molecule, which has small but non-zero tangle. The crosses show the energy calculated at each experimental step, assuming an ideal quantum device. (b) Overlap |‹ψ^j|ψ^G› between the experimentally computed state |ψ^j› at each optimization step j and the theoretical ground state of , |ψ^G›. Error bars are smaller than the data points. Further details are provided in the Methods section, Supplementary Table 1 and Supplementary Methods.