Multipartite spin entanglement from many-electron systems

Estimation of entanglement in atomistic systems requires a combination of advanced ab initio calculations - to account for the effect of the electron-electron interaction - and rigorous quantum-informational theoretical analyses. This combination is a challenging task that has not been tackled so far to investigate genuine multipartite entanglement (GME) in materials. Here we show that, contrary to conventional wisdom, a high degree of GME between spins can be extracted from closed-shell molecular states - even in the non-interacting limit (single-configuration states). This applies both to prototypical cases, designed to reproduce a target spin-ring ground state, and for realistic ground states of diverse molecules, including benzene. In the latter case, close to maximal values of the GME concurrence have been obtained with a physically motivated — rather than an arbitrary or ad hoc — choice of localized orbitals. Because the relevant states fulfill the super-selection rules, the generated entanglement may in principle represent also a physical resource.