Analytical recursive method to ascertain multisite entanglement in doped   quantum spin ladders
  We formulate an analytical recursive method to generate the wave function of doped short-range resonating valence bond (RVB) states as a tool to efficiently estimate multisite entanglement as well as other physical quantities in doped quantum spin ladders. We prove that doped RVB ladder states are always genuine multipartite entangled. Importantly, our results show that within specific doping concentration and model parameter regimes, the doped RVB state essentially characterizes the trends of genuine multiparty entanglement in the exact ground states of the Hubbard model with large onsite interactions, in the limit which yields the $t$-$J$ Hamiltonian. 
Sudipto Singha Roy, Himadri Shekhar Dhar, Debraj Rakshit, Aditi Sen   De, Ujjwal Sen
quant-ph cond-mat.str-el