Dissociation of ultracold molecules with Feshbach resonances

Ultracold molecules are associated from an atomic Bose-Einstein condensate by ramping a magnetic field across a Feshbach resonance. The reverse ramp dissociates the molecules. The kinetic energy released in the dissociation process is used to measure the widths of four Feshbach resonances in ${}^{87}\mathrm{Rb}$. This method to determine the width works remarkably well for narrow resonances even in the presence of significant magnetic-field noise. In addition, a quasimonoenergetic atomic wave is created by jumping the magnetic field across the Feshbach resonance.

Figure 1

Mean kinetic energy per atom as a function of the speed of the dissociation ramp. Parts (a), (b), (c), and (d) were measured at Feshbach resonances at 632, 685, 912, and $1007\mathrm{G}$, respectively. The solid lines show fits of Eq. (3) to the data. The best-fit values are shown in Table .

Figure 2

(Color online) (a) Monoenergetic spherical wave of atoms, created by dissociation of molecules when jumping the magnetic field across the Feshbach resonance. The atoms fly apart on the surface of a hollow sphere. The absorption-imaging beam integrates the three-dimensional density profile along one direction. The observed two-dimensional image therefore shows a ring, with a nonzero density in the center. The image was averaged over $\sim 100$ experimental shots. (b) Line profile across the center of the image. The dip in the center is clearly visible.