Entanglement spectrum of one-dimensional extended Bose-Hubbard models

The entanglement spectrum provides crucial information about correlated quantum systems. We show that the study of the blocklike nature of the reduced density matrix in number sectors and the partition dependence of the spectrum in finite systems leads to interesting unexpected insights, which we illustrate for the case of a one-dimensional extended Hubbard model. We show that block symmetry provides an intuitive understanding of the spectral double degeneracy of the Haldane insulator, which is remarkably maintained at low on-site interaction, where triple or higher site occupation is significant and particle-hole symmetry is broken. Moreover, surprisingly, the partition dependence of the spectral degeneracy in the Haldane insulator, and of a partial degeneracy in the Mott insulator, is directly linked to the, in principle unrelated, density-density correlations, and presents an intriguing periodic behavior in superfluid and supersolid phases.