Association of Efimov Trimers from a Three-Atom Continuum

We develop an experimental technique for rf association of Efimov trimers from a three-atom continuum. We apply it to probe the lowest accessible Efimov energy level in bosonic lithium in the region where strong deviations from the universal behavior are expected, and provide a quantitative study of this effect. The position of the Efimov resonance at the atom-dimer threshold, measured using a different experimental technique, concurs with the rf association results.

Figure 1

(a) Dimer (solid blue) and trimer (dotted-dashed pink) energy levels as calculated using the universal theory [1] with $a_{*}=288a_0$, where $a_0$ is the Bohr radius. This value is expected from the previously measured three-body recombination spectrum[15, 31]. (b) The difference between the dimer and trimer energy levels for two different Efimov resonances at the atom-dimer threshold: $a_{*}=288a_0$ (solid green) and $a_{*}=200a_0$ (dashed red).

Figure 2

rf-induced atom loss resonances for different values of the dimer binding energy. For the weakly bound dimer [(a)–(c)] strongly overlapped double-peak loss structures are clearly visible. For the deeper bound dimer (d) only a single minimum is observed, signifying that the dimer and the trimer energy levels converged to a value below the resolution limit. Each point is an average of 3 to 5 individual measurements. Solid lines represent the double-peak Gaussian fits to the data.

Figure 3

The difference between trimer and dimer energies as a function of the dimer energy level. The points represent results of fits to the measurements with double-peak Gaussian distributions. The error bars show 1 standard deviation of the fit. The solid line represents the prediction made by universal theory for $a_{*}=288a_0$. The dashed red line shows the fit of universal theory with an additional fitting parameter—the multiplication factor of the energy difference $\delta E$. The dotted horizontal line marks the minimal $\delta E$ that can be reliably detected due to the resolution limit.

Figure 4

The three-body recombination spectrum. Only the positive range of $a$ is shown. In addition to the earlier published minimum in $K_3(a)$ [15] there is a local maximum (enlarged in the inset) that we attribute to a secondary collision resonance which indicates the position of the Efimov resonance at the atom-dimer threshold $a_e^{*}\approx 200a_0$. The solid line in the inset is a fit to the model of secondary collisions [34].