Two Atomic Species Superfluid

We produce a quantum degenerate mixture composed by two Bose-Einstein condensates of different atomic species, ${}^{\mathrm{41}}\mathrm{K}$ and ${}^{\mathrm{87}}\mathrm{R}\mathrm{b}$. We study the dynamics of the superfluid system in an elongated magnetic trap, where off-axis collisions between the two interacting condensates induce scissorlike oscillations.

Figure 1

Absorption imaging of a binary ${}^{\mathrm{41}}\mathrm{K}\mathrm{\text{−}}{}^{\mathrm{87}}\mathrm{R}\mathrm{b}$ Bose-Einstein condensate after 13 ms of ballistic expansion: (a) at $T\simeq 100\mathrm{n}\mathrm{K}$ the Rb sample is still thermal; (b) at $T\le 80\mathrm{n}\mathrm{K}$ both species are condensed. (c) Enlarged view of the density profile of the binary BEC in the magnetic trap in the Thomas-Fermi approximation. The two centers of mass are displaced by gravity.

Figure 2

Dipolar oscillations of the K and Rb condensates along the $z$ axis, induced by a modification of the radial trap confinement. Center-of-mass position of (a) K and (b) Rb after the ballistic expansion; the dots are the experimental data, while the continuous lines are a simulation using the GPE. (c) Calculated evolution of the center-of-mass position for K (solid line) and Rb (dotted line) in the trap.

Figure 3

Collision-induced rotation of the binary BEC during the dipolar oscillations. The first three images correspond to an evolution time in the trap: (a) 8 ms; (b) 8.5 ms; (c) 9 ms. In (d) the evolution time is 8 ms as in (a), but the Rb BEC has been removed before the excitation of the dipolar oscillations; no rotation is observed in this case.

Figure 4

(a) Evolution of the angle of rotation of the K BEC from the vertical direction, after a 13 ms ballistic expansion. The dotted line is a guide to the eye and the error bar indicates the typical experimental uncertainty. (b) Numerical simulation using the GPE of the angular velocity of the condensate at release from the trap.