Tunable Miscibility in a Dual-Species Bose-Einstein Condensate

Abstract

We report on the observation of controllable phase separation in a dual-species Bose-Einstein condensate with 85 Rb and 87 Rb. Interatomic interactions between the different components determine the miscibility of the two quantum fluids. In our experiments, we can clearly observe immiscible behavior via a dramatic spatial separation of the two species. Furthermore, a magnetic-field Feshbach resonance is used to change them between miscible and immiscible by tuning the 85 Rb scattering length. The spatial density pattern of the immiscible quantum fluids exhibits complex alternating-domain structures that are uncharacteristic of its stationary ground state. . Ultracold quantum gases also provide a unique opportunity to study the miscibility of interpenetrating quantum fluids. They exhibit numerous advantages including the resonant control of two-body interactions via magnetic-field Feshbach resonances, which provides a parameter to directly alter the miscibility of the fluids.The first two-component condensate was produced with different hyperfine states of 87 Rb, and evidence for repulsive interactions between the two clouds was reported [2]. The dynamical behavior of a two-component BoseEinstein condensate (BEC) has been studied extensively [3,4] including the dramatic observation of weakly damped collective oscillations [5]. In spinor condensates both miscible and immiscible two-component condensates were observed for the first time [6]. They formed long-lived metastable excited states composed of magnetic domains [7], and tunneling effects between the domains were studied [8]. Dual-species quantum gases are currently a subject of significant interest. In particular, an outstanding goal is the creation of ultracold heteronuclear molecules in low-lying vibrational states. Such molecules are expected to possess a dipole moment that could be utilized for such varied applications as quantum information and the search for the electron electric dipole moment [9]. A dual-species BEC of 41 K and 87 Rb has already been realized in a harmonic potential [10] and in an optical lattice [11]. In a Bose-Fermi mixture of 40 K and 87 Rb, a tunable interspecies scattering length was used to probe both phase separation of the mixture and interaction-induced collapse [12].Understanding how the spatial overlap of a dual-species BEC changes as interactions are tuned will be important for future experiments. In this Letter, we explore the tunable miscibility of a Bose-condensed mixture of 85 Rb and 87 Rb gases. Immiscibility of the two-component quantum gas is observed as a dramatic departure of the density distribution from the symmetry of the trapping potential. Surprisingly, we observe the robust formation of multiple, nonoverlapped, single-species BEC ''cloudlets'' that represent an interesting presumably metastable excited state.Theoretical investigations of two-component condensates have illuminated the role that interatomic interactions play in determining the density patterns and phase separation of the components [13][14][15...

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.…”

“…Possible experimental implementations of the results discussed in this paper could be made by considering 85 Rb − 87 Rb boson-boson mixtures loaded in the deep optical lattices [27,29,30]. The inter-species scattering length can be varied in time by means of the Feshbach resonance technics (see the recent review [22] and references therein).…”

“…where the combinations of signs, (−, −), (+, +) in front of the terms κ 1 , κ 2 , refer to the in-phase and out-of-phase compactons, respectively, while the other combinations (−, +) and (+, −), refer to mixed-symmetry compactons in (27), (28), respectively. Typical result for the in-phase and out-of-phase two-site B-B compactons are shown on Fig.…”

“…(25) and (26) refer to the in-phase and out-of-phase compactons, respectively, while Eqs. (27) and (28) to compactons of mixed-symmetry type. By substituting the above expressions into Eqs.…”

Species-selective confinement of atoms dressed with multiple radiofrequencies

“…Experiments have demonstrated tunable interactions in 85 Rb [46], the sympathetic cooling of 85 Rb with 87 Rb [47], the formation of ultracold molecules [7] and the controllable miscibility of two condensates [48]. More recently, this mixture has been used in atom interferometry experiments where a second species can be used to remove common mode noise or test the weak equivalence principle [49][50][51][52][53][54].…”