Double Species Bose-Einstein Condensate with Tunable Interspecies Interactions

Abstract

We produce Bose-Einstein condensates of two different species, 87 Rb and 41 K, in an optical dipole trap in proximity of interspecies Feshbach resonances. We discover and characterize two Feshbach resonances, located around 35 and 79 G, by observing the three-body losses and the elastic crosssection. The narrower resonance is exploited to create a double species condensate with tunable interactions. Our system opens the way to the exploration of double species Mott insulators and, more in general, of the quantum phase diagram of the two species Bose-Hubbard model. Ultracold atomic gases seem uniquely suited to experimentally realize and investigate physics long studied in the domain of condensed matter and solid state physics, with the distinct advantage that specific effects are better isolated from unnecessary complications often present in condensed samples. The paradigmatic superfluid to Mott insulator transition of a condensate in an optical lattice [1] confirmed the predictions of the Bose-Hubbard model [2,3], originally introduced to describe superfluid Helium. With two species, the zero-temperature diagram of quantum phases is much richer than the simple duplication of the single species ' [4]. Indeed it has been proposed that two species obeying an extended BoseHubbard model can mimick the physics of lattice spins described by the Heinsenberg model [5,6] and give rise to yet unobserved quantum phases, like the double Mott insulator and the supercounterflow regime [7], with peculiar transport properties. Therefore, a double species condensate in an optical lattice stands as a promising candidate system for quantum simulations. Recently, the investigation of the two-species BH was started from the regime where one species exhibits the loss of phase coherence usually associated with the Mott insulator transition, while the other is completely delocalized [8]. Already at this stage, the presence of two species leads to a surprising shift of the critical point, which is now object of intense theoretical work [9].In addition, a double Mott insulator is expectedly extremely useful to produce heteronuclear polar molecules [10], since the association efficiency strongly depends on the phase space overlap of the two species [11]. The rapid losses of associated molecules observed for bosonic systems could be largely suppressed by the presence of the three-dimensional optical lattice [12], if most of the sites are occupied with only one atom per species. Both these research avenues require the dynamic control of interspecies interactions, along with a well established collisional model.

Vortex sheet in rotating two-component Bose-Einstein condensates

“…The typical example is phase separation of the binary BEC mixtures, where each component separates spatially due to the strong intercomponent repulsion. Several experiments have observed this phase separation [6,7,8,9,10,11], supported by the numerous theoretical studies [12,13,14,15,16,17,18,19]. We can now control miscibility or immiscibility of the two-component BEC, because intercomponent interaction is tunable by changing the s-wave scattering length via a Feshbach resonance, as demonstrated recently [10,11].…”

Distinguishability, degeneracy, and correlations in three harmonically trapped bosons in one dimension

“…For example, in certain interacting limits, their ground-state wave function can be obtained analytically and it is similar to a TG gas for both components [24,25]. The intra-and interspecies interactions, which describe all the interaction processes in these mixtures, can be controlled experimentally by means of Feshbach and confinement induced resonances [26][27][28]. By playing with both the intra-and interspecies interactions one can explore different physical phenomena, like phase separation on small atom mixtures [29][30][31][32][33].…”

Bose-Hubbard model with random impurities: Multiband and nonlinear hopping effects

“…The shift of the observed transition between the superfluid (SF) and the MI phases, observed experimentally in Refs. [38][39][40] (for the analogous effects with Bose-Bose mixtures and tightly trapped bosons, see [41,42]), could not be explained with this simple description. It has soon been realized that density-dependent tunneling terms as well as contributions coming from higher Bloch bands are necessary to describe the systems in question [43][44][45][46], whenever the interspecies interaction becomes strong enough.…”