Mott-insulator phases of nonlocally coupled one-dimensional dipolar Bose gases

Abstract

We analyze the Mott-insulator phases of dipolar bosonic gases placed in neighboring but unconnected 1D traps. Whereas for short-range interactions the 1D systems are independent, the non-local dipole-dipole interaction induces a direct Mott-insulator to pair-superfluid transition which significantly modifies the boundaries of the lowest Mott-insulator phases. The lowest boundary of the lowest Mott regions becomes progressively constant as a function of the hopping rate, eventually inverting its slope, leading to a re-entrant configuration which is retained in 2D. We discuss the consequences of this effect on the spatial Mott-insulator plateaux in experiments with additional harmonic confinement, showing that anti-intuitively the plateaux may become wider for increasing hopping. Our results are also applicable to non-dipolar boson-boson mixtures. U 0 J U 0 −|U'| J

Superfluid–Mott-insulator transition in the spin-orbit-coupled Bose-Hubbard model

“…However, this definition of the SF phase does not discriminate the possibility of exotic multiparticle and/or multihole excitations that may be gapless; our MI lobes may still have some sort of hidden SF orders. For instance, in the absence of SOC and Zeeman field, it is already known that a counterflow-SF phase of particle-hole pairs [24,25,29,31] characterized by the order parameter j ≡ â j ↑â † j ↓ and a paired SF phase of two particles or two holes [25,[28][29][30][31] characterized by the order parameter j ≡ â j ↑âj ↓ are possible when U ↑↓ > 0 and U ↑↓ < 0, respectively [31]. The effects of SOC and/or Zeeman field on the fates of such exotic SF phases is uncharted territory.…”

“…In this context, the two-component Bose-Hubbard model [24][25][26][27][28][29][30][31] was introduced about a decade ago to describe cold-atom experiments involving two types of bosons, in which the two components may correspond to different hyperfine states of a particular atom or different species of atoms. In addition to the phases that are similar in many ways to the MI and SF phases of the single-component model, these works proposed that paired-SF, counterflow-SF, density-wave insulator, and supersolid phases may be created with the experimental realization of the two-component model.…”

Mean-field theory for the Mott-insulator–paired-superfluid phase transition in the two-species Bose-Hubbard model

“…For sufficiently attractive U ↑↓ , it is well established that [6][7][8][9][10][11] instead of a direct transition from the Mott insulator to a single-particle superfluid phase, the transition is from the Mott insulator to a paired-superfluid phase (superfluidity of composite bosons, i.e., Bose-Bose pairs). In fact, in the limit when {t ↑ ,t ↓ } → 0, it can be shown that the transition is from the Mott insulator to a paired-superfluid phase for all U ↑↓ < 0 [12].…”

“…Among them the two-species Bose-Hubbard model, which can be studied with two-component Bose gases loaded into optical lattices, is one of the most popular. This is because, in addition to the Mott-insulator and single-speciessuperfluid phases, it has been predicted that this model has at least two additional phases: an incompressible super-counter flow and a compressible paired-superfluid phase [6][7][8][9][10][11].…”

“…Among them the two-species Bose-Hubbard model, which can be studied with two-component Bose gases loaded into optical lattices, is one of the most popular. This is because, in addition to the Mott-insulator and single-speciessuperfluid phases, it has been predicted that this model has at least two additional phases: an incompressible super-counter flow and a compressible paired-superfluid phase [6][7][8][9][10][11].Our main interest here is in the latter phase, where a direct transition from the Mott-insulator phase to the pairedsuperfluid phase (superfluidity of composite bosons, i.e., Bose-Bose pairs) has been predicted, when both species have integer fillings and the interspecies interaction is sufficiently large and attractive. In this paper, we derive an analytic mean-field expression for the Mott-insulator-paired-superfluid transition boundary in the two-species Bose-Hubbard model.…”