Two Atomic Species Superfluid

Abstract

We produce a quantum degenerate mixture composed by two Bose-Einstein condensates of different atomic species, 41 K and 87 Rb. We study the dynamics of the superfluid system in an elongated magnetic trap, where off-axis collisions between the two interacting condensates induce scissors-like oscillation.The long-standing interest in mixtures of superfluids, originally focused on helium systems [1], has recently been renewed by the achievement of Bose Einstein condensation (BEC) in dilute atomic gases [2]. Already using a single atomic species, multiple condensates were realized by exploiting the magnetic structure of the ground electronic state of alkali atoms. Mixtures of two hyperfine spin states of 87 Rb in magnetic traps allowed to study the effect of the mutual interaction in the dynamic of miscible BECs [3]. Superposition of spinor condensates of 23 Na in an optical trap led to a first observation of both weakly miscible and immiscible superfluids [4] and of the occurrence of metastable states [5]. These experimental achievements stimulated an extensive theoretical research on the properties of a mixture of two BECs, and the role of the interparticle interaction in determining its static and dynamical properties has been recognized [6][7][8][9][10].As early suggested [6], an even wider scenario for the study of superfluid systems would be opened by BEC in mixtures of different atoms. Considering the species condensed so far, the use of different isotopes of the same species would be restricted to the case of rubidium [11], while a wider choice would be offered the use of different atomic species. Recently, two-species mixtures were successful for the realization of Fermi-Bose degenerate gases [12].In this Letter, we report the realization of a mixture of Bose-Einstein condensates of different atomic species, using potassium and rubidium. Simultaneous condensation of 41 K and 87 Rb is achieved by means of two-species sympathetic cooling [13] in a magnetic trap. The stability against collapse of the degenerate mixture, already * also at

Feshbach spectroscopy of aK−Rbatomic mixture

“…It is otherwise neither consistent with the determination of [19] nor with the observation of a collapse instability in this mixture [27,28]. Comparison of the collapse observations reported so far with current mean-field models indicated a t = (−395 ± 15)a 0 for [27] (see the analysis in [5]) and (-281±15)a 0 for [28]. These discrepancies with the current determination could be in principle explained by a lowfield Feshbach resonance in the magnetically trappable state |9/2, 9/2 +|2, 2 used in those experiments, which however seems to be excluded by our collisional model.…”

“…32.80.Pj; Quantum degenerate atomic mixtures [1,2,3,4,5,6] are promising for the study of a variety of novel physical phenomena, such as production of quantum gases of polar molecules [7], boson-induced superfluidity of fermions [8], and quantum phases of matter in optical lattices [9] or random potentials [10]. The study of these phenomena requires the use of magnetically tunable Feshbach resonances [11] to control the interaction.…”

Bouncing motion and penetration dynamics in multicomponent Bose-Einstein condensates

“…In contrast to previous experiments on collisions between BECs in a magnetic trap [7,26], the use of an optical trap enabled us to generate multicomponent BECs with various degrees of miscibility. The observed dynamics are classified into two categories: repeated bouncing motion and mutual penetration after damped bouncing motion.…”

“…In multicomponent BECs, the miscibility is determined by inter-and intra-species atomic interaction strengths [1] and, importantly, they can be experimentally controlled using Feshbach resonances [2,3] and Rabi coupling [4,5]. Multicomponent BECs with various degrees of miscibility are also available by choosing the internal states [6] or atomic species [7]. Employing such adjustability and selectability, intriguing phenomena that depend on the degree of miscibility have been experimentally observed, e.g., soliton generation in a counterflow of miscible fluids [8,9] The condition for miscibility in multicomponent BECs is determined by linear stability analysis of a static or steady state, and is not naively applicable to dynamical situations.…”

Binary matter-wave compactons induced by inter-species scattering length modulations

“…Example of boson-boson mixtures which can be considered are 39 K-87 Rb, 41 K-87 Rb, 85 Rb-87 Rb. At the present binary BEC mixtures are observed for the system 85 Rb-87 Rb [27] and 41 K − 87 Rb [28]. The inter-species scattering length can be varied in time by means of the Feshbach resonance technics.…”