Molecular nanomagnets (MNMs) are molecules containing a core of magnetic ions whose spins are strongly coupled by superexchange interactions. Being among the first examples of finite-size spin systems, MNMs have been test beds for addressing several quantum phenomena. A great advantage of these systems is that their spin Hamiltonian can be chemically engineered to meet specific requirements. In particular, exploiting the spin dynamics of MNMs for quantum information processing is currently a major research goal.
Entanglement is a crucial resource for quantum information processing and its detection and quantification is of paramount importance in many areas of current research. Weakly coupled MNMs provide an ideal test bed for investigating entanglement between complex spin systems. However, entanglement in these systems had only been experimentally demonstrated rather indirectly by macroscopic techniques or by fitting trial model Hamiltonians to experimental data.
In this talk, I show that four-dimensional inelastic neutron scattering  enables us to portray entanglement in weakly coupled molecular qubits and to quantify it . We have used the cold neutron time-of-flight spectrometer IN5 at the Institute ILL in Grenoble to investigate the prototype (Cr7Ni)2 supramolecular dimer. By exploiting this system as a benchmark, we have demonstrated the potential of this approach, which allows one to extract the concurrence in eigenstates of a dimer of molecular qubits without diagonalizing its full Hamiltonian.
 Spin dynamics of molecular nanomagnets unravelled at atomic scale by four-dimensional inelastic neutron scattering, M. L. Baker, T. Guidi, S. Carretta, J. Ollivier, H. Mutka, H. U. Güdel, G. A. Timco, Eric J. L. McInnes, G. Amoretti, R. E. P.Winpenny, P. Santini, Nature Physics 8, 906 (2012).
 Portraying entanglement between molecular qubits with four-dimensional inelastic neutron scattering, E. Garlatti, T. Guidi, S. Ansbro, P. Santini, G. Amoretti, J. Ollivier, H. Mutka, G. Timco, I.J. Vitorica-Yrezabal, G.F.S. Whitehead, R.E.P. Winpenny, S. Carretta, Nature Communications 8, 14543 (2017).