Degenerate Bose-Bose mixture in a three-dimensional optical lattice

We produce a heteronuclear quantum degenerate mixture of two bosonic species, ${}^{87}\mathrm{Rb}$ and ${}^{41}\mathrm{K}$, in a three-dimensional optical lattice. On raising the lattice barriers, we observe the disappearance of the inference pattern of the heavier ${}^{87}\mathrm{Rb}$, shifting toward shallower lattice depths in the presence of a minor fraction of ${}^{41}\mathrm{K}$. This effect is sizable and requires only a marginal overlap between the two species. We compare our results with similar findings reported for Fermi-Bose mixtures and discuss the interpretation scenarios proposed to date, arguing that the explanation may be linked to the increased effective mass due to the interspecies interactions.

Figure 1

(Color online) Interference pattern of ${}^{87}\mathrm{Rb}$ for $s=6,11,16$ (left to right). Upper row: ${}^{87}\mathrm{Rb}$ only; lower row: ${}^{87}\mathrm{Rb}$ mixed with ${}^{41}\mathrm{K}$ (not shown). Each panel represents the column density over an area $175\times 135\mu {\mathrm{m}}^2$.

Figure 2

(Color online) Visibility and width of the central peak of the ${}^{87}\mathrm{Rb}$ interference pattern, for partial (a),(c) and zero (b),(d) overlap with the ${}^{41}\mathrm{K}$ condensate. In each panel we compare data and fit (dashed lines) with ${}^{41}\mathrm{K}$ atoms [red (gray)] and without (black), i.e., with $N_K=2\left(1\right)\times {10}^3$ and 0. The insets show how visibility of ${}^{87}\mathrm{Rb}$ is extracted from images (e) and the interference pattern of ${}^{41}\mathrm{K}$ visible for $s=20$ (f).

Figure 3

(Color online) Density distribution of ${}^{87}\mathrm{Rb}$ (red, left) and ${}^{41}\mathrm{K}$ (blue, right) atoms, in the plane $z=0$, calculated by numerical integration of the GPE: $N_{\mathrm{Rb}}=3\times {10}^4$, $N_{\mathrm{K}}=2\times {10}^3$, vertical lattice strength $s=11$. Hatched area (green) highlights the overlap, while the inset plot reports density profiles along the vertical line through $x=0$.

Figure 4

(Color online) Visibility of the fringes at $s=12$ versus the duration of the lattice ramp up.