Comment on "Regional Versus Global Entanglement in Resonating-Valence-Bond States"

Fabien Alet (1, 2) , Daniel Braun (3) , Grégoire Misguich (4)

1 FFC - Fermions Fortement Corrélés (LPT)
2 LPT - Laboratoire de Physique Théorique
3 ICQ - Cohérence Quantique (LPT)
4 IPHT - Institut de Physique Théorique - UMR CNRS 3681

In a recent Letter [Phys. Rev. Lett. 99, 170502 (2007); quant-ph/0703227], Chandran and coworkers study the entanglement properties of valence bond (VB) states. Their main result is that VB states do not contain (or only an insignificant amount of) two-site entanglement, whereas they possess multi-body entanglement. Two examples ("RVB gas and liquid") are given to illustrate this claim, which essentially comes from a lower bound derived for spin correlators in VB states. We show in this Comment that (i) for the "RVB liquid" on the square lattice, the calculations and conclusions of Chandran et al. are incorrect. (ii) A simple analytical calculation gives the exact value of the correlator for the "RVB gas", showing that the bound found by Chandran et al. is tight. (iii) The lower bound for spin correlators in VB states is equivalent to a celebrated result of Anderson dating from more than 50 years ago.

Domaines: Physique Quantique [quant-ph]; Electrons fortement corrélés [cond-mat.str-el]

Fabien Alet, Daniel Braun, Grégoire Misguich. Comment on "Regional Versus Global Entanglement in Resonating-Valence-Bond States". Physical Review Letters, 2008, 101, pp.248901. ⟨10.1103/PhysRevLett.101.248901⟩. ⟨hal-00346646⟩