Mesoscopic Ensembles of Polar Bosons in Triple-Well Potentials

Abstract

Mesoscopic dipolar Bose gases in triple-well potentials offer a minimal system for the analysis of the non-local character of the dipolar interaction. We show that this non-local character may be clearly revealed by a variety of possible ground-state phases. In addition, an appropriate control of short-range and dipolar interactions may lead to novel scenarios for the dynamics of polar bosons in lattices, including the dynamical creation of mesoscopic quantum superpositions, which may be employed in the design of Heisenberg-limited atom interferometers.PACS numbers: 03.75. Kk,03.75.Lm Interparticle interactions are crucial in quantum gases [1]. They can usually be described by a short-range isotropic potential proportional to the scattering length a. Recently, dipolar quantum gases, in which the longrange and anisotropic dipole-dipole interaction (DDI) between magnetic or electric dipole moments plays a significant or even dominant role, have attracted a lot of interest as they show fascinating novel properties [2,3]. To date, dipolar effects have been observed experimentally only with atomic magnetic dipoles, being particularly relevant in Bose-Einstein condensates (BECs) of 52 Cr where exciting new physics has been observed [4][5][6][7]. Dipolar effects have also been reported in spinor BECs [8], and in 39 K and 7 Li BECs with a = 0 [9, 10]. Recent experiments with polar molecules [11,12] open fascinating perspectives towards the realization of highly-dipolar gases.Although a very clear and direct demonstration of the anisotropy of the DDI was given by the d-wave collapse of a Cr-BEC [6,7], an equivalently obvious 'visual' proof of the non-local character of the DDI is still missing. Such a non-ambiguous qualitative evidence of the non-local character of the dipolar interaction could be provided in principle by the observation of novel quantum phases (supersolid, checkerboard) in optical lattices [13]. However, the unambiguous detection of such phases is far from trivial, as is the preparation of the ground state of the system due to a large number of metastable states [14].In this Letter, we investigate a minimal system, namely a mesoscopic sample of dipolar bosons in a triple-well potential, which minimizes these restrictions, while still presenting clear visual non-local features (see "phase" B below). Non-dipolar BECs in double-well potentials have allowed for the observation of Josephson oscillations and non-linear self trapping [15], showing clearly that 'slicing' a BEC dramatically enhances the effects of interactions. The two-well Josephson physics is affected quantitatively (although not qualitatively) by the DDI [16,17] (the DDI may induce however significant inter-site effects in coupled 1D and 2D bilayer systems [18][19][20]). On the contrary, as we show below, the DDI does introduce qualitatively novel physics in the Josephson-like dynamics in three-well systems. We discuss how the DDI leads to various possible ground states, which may visually reveal the non-locality of the DDI. In addition, w...

Supersolid phase in atomic gases with magnetic dipole interaction

“…This argument coincides with the observation, that n excitations with an energy nV per lattice site are required for the disappearance of the solid order. Consequently, this transition temperature is strongly increased compared to the single-particle nearest-neighbor energy V , and it is in agreement with the formation of solid structures in very large superlattices [21].…”

Directed selective tunneling of dipolar bosons in a driven triple well

“…These results presented in our paper may be employed in the design of a single-atom source and atomic transistor [14,15,28,29]. U 2 describes the interact between nonadjacent atoms, where the ratio of the nearest-neighbor and next-nearest-neighbor interaction 4 U 1 /U 2 8 [20,21]. We choose the driving field ε(t) = ε 0 + ε 1 cos(ωt) with ε 0 being the strength of dc field, ε 1 and ω the strength and frequency of the ac field.…”

“…In recent discussions, the triple-well potential with one-dimensional configuration, a minimal system loaded with a dipolar gas for discussing the effect of DDI, was studied extensively. For example, a variety of possible ground-state phases were revealed and the dynamical creation of mesoscopic quantum superpositions was discussed [20]. Because of the intersite interaction, the nonlocal coherence was studied [21].…”

Modification of roton instability due to the presence of a second dipolar Bose-Einstein condensate

“…The transition from the macroscopic quantum self-trapping to the Josephson oscillation regime has been interpreted using a single twomode model that treats the left well and the right well as being occupied by macroscopic wavefunctions 1 and 2 , respectively. Extensions to triple-well potentials, which provide a simplifying model of an optical lattice system, have also been considered [21]. Here we model a two-well dipolar system, for which tunneling is assumed to be negligible, and solve a set of two coupled Gross-Pitaevskii (GP) and Bogoliubov-de Gennes (BdG) equations.…”