Correlations of strongly interacting ultracold dipolar bosons in optical lattices
Strongly interacting dipolar bosons in optical lattices exhibit diverse quantum phases that are rich in physics. As the strength of the long-range boson-boson interaction increases, the system transitions across different phases: from a superfluid, through a Mott-insulator to a Tonks gas and, eventually, a crystal state. The signature of these phases and their transitions can be unequivocally identified by an experimentally detectable order parameter, recently described in arXiv:1708.07409. Herein, we calculate the momentum distributions and the normalized Glauber correlation functions of dipolar bosons in a one-dimensional optical lattice in order to characterize all their phases. To understand the behavior of the correlations across the phase transitions, we first investigate the eigenfunctions and eigenvalues of the one-body reduced density matrix as the function of the dipolar interaction strength. We then analyze the real- and momentum-space Glauber correlation functions, thereby gaining a spatially and momentum-resolved insight into the coherence properties of these quantum phases. We find an intriguing structure of non-local correlations that, independently of other system parameters, reveal the phase transitions of the system. In particular, spatial localization with synchronous momentum delocalization accompanies the formation of correlated islands in the density. Moreover, our study showcases that precise control of intersite correlations is possible through manipulation of the depth of the lattice, while intrasite correlations are influenced solely by changing the dipolar interaction strength.