Finite size mean-field models

M Fannes, C Vandenplas
2006 Journal of Physics A: Mathematical and General  
We characterize the two-site marginals of exchangeable states of a system of quantum spins in terms of a simple positivity condition. This result is used in two applications. We first show that the distance between two-site marginals of permutation invariant states on N spins and exchangeable states is of order 1/N. The second application relates the mean ground state energy of a mean-field model of composite spins interacting through a product pair interaction with the mean ground state energies of the components.
doi:10.1088/0305-4470/39/45/001 fatcat:7ita425gyzaj5lwrbih6jr235m